FEATURE: Rename 'Discourse SSO' to DiscourseConnect (#11978)

The 'Discourse SSO' protocol is being rebranded to DiscourseConnect. This should help to reduce confusion when 'SSO' is used in the generic sense.

This commit aims to:
- Rename `sso_` site settings. DiscourseConnect specific ones are prefixed `discourse_connect_`. Generic settings are prefixed `auth_`
- Add (server-side-only) backwards compatibility for the old setting names, with deprecation notices
- Copy `site_settings` database records to the new names
- Rename relevant translation keys
- Update relevant translations

This commit does **not** aim to:
- Rename any Ruby classes or methods. This might be done in a future commit
- Change any URLs. This would break existing integrations
- Make any changes to the protocol. This would break existing integrations
- Change any functionality. Further normalization across DiscourseConnect and other auth methods will be done separately

The risks are:
- There is no backwards compatibility for site settings on the client-side. Accessing auth-related site settings in Javascript is fairly rare, and an error on the client side would not be security-critical.
- If a plugin is monkey-patching parts of the auth process, changes to locale keys could cause broken error messages. This should also be unlikely. The old site setting names remain functional, so security-related overrides will remain working.

A follow-up commit will be made with a post-deploy migration to delete the old `site_settings` rows.

app/models/discourse_single_sign_on.rb

@@ -6,11 +6,11 @@ class DiscourseSingleSignOn < SingleSignOn
   class BannedExternalId < StandardError; end
 
   def self.sso_url
-    SiteSetting.sso_url
+    SiteSetting.discourse_connect_url
   end
 
   def self.sso_secret
-    SiteSetting.sso_secret
+    SiteSetting.discourse_connect_secret
   end
 
   def self.generate_sso(return_path = "/")
@@ -120,7 +120,7 @@ class DiscourseSingleSignOn < SingleSignOn
     # The user might require approval
     user.create_reviewable
 
-    if bio && (user.user_profile.bio_raw.blank? || SiteSetting.sso_overrides_bio)
+    if bio && (user.user_profile.bio_raw.blank? || SiteSetting.discourse_connect_overrides_bio)
       user.user_profile.bio_raw = bio
       user.user_profile.save!
     end
@@ -170,7 +170,7 @@ class DiscourseSingleSignOn < SingleSignOn
   end
 
   def apply_group_rules(user)
-    if SiteSetting.sso_overrides_groups
+    if SiteSetting.discourse_connect_overrides_groups
       synchronize_groups(user)
       return
     end
@@ -219,7 +219,7 @@ class DiscourseSingleSignOn < SingleSignOn
 
         user = User.create!(user_params)
 
-        if SiteSetting.verbose_sso_logging
+        if SiteSetting.verbose_discourse_connect_logging
           Rails.logger.warn("Verbose SSO log: New User (user_id: #{user.id}) Params: #{user_params} User Params: #{user.attributes} User Errors: #{user.errors.full_messages} Email: #{user.primary_email.attributes} Email Error: #{user.primary_email.errors.full_messages}")
         end
       end
@@ -233,7 +233,7 @@ class DiscourseSingleSignOn < SingleSignOn
             Jobs.enqueue(:download_avatar_from_url,
               url: avatar_url,
               user_id: user.id,
-              override_gravatar: SiteSetting.sso_overrides_avatar
+              override_gravatar: SiteSetting.discourse_connect_overrides_avatar
             )
           end
 
@@ -273,13 +273,13 @@ class DiscourseSingleSignOn < SingleSignOn
   def change_external_attributes_and_override(sso_record, user)
     @email_changed = false
 
-    if SiteSetting.sso_overrides_email && user.email != Email.downcase(email)
+    if SiteSetting.auth_overrides_email && user.email != Email.downcase(email)
       user.email = email
       user.active = false if require_activation
       @email_changed = true
     end
 
-    if SiteSetting.sso_overrides_username? && username.present?
+    if SiteSetting.auth_overrides_username? && username.present?
       if user.username.downcase == username.downcase
         user.username = username # there may be a change of case
       elsif user.username != username
@@ -287,7 +287,7 @@ class DiscourseSingleSignOn < SingleSignOn
       end
     end
 
-    if SiteSetting.sso_overrides_name && user.name != name && name.present?
+    if SiteSetting.auth_overrides_name && user.name != name && name.present?
       user.name = name || User.suggest_name(username.blank? ? email : username)
     end
 
@@ -297,18 +297,18 @@ class DiscourseSingleSignOn < SingleSignOn
 
     avatar_missing = user.uploaded_avatar_id.nil? || !Upload.exists?(user.uploaded_avatar_id)
 
-    if (avatar_missing || avatar_force_update || SiteSetting.sso_overrides_avatar) && avatar_url.present?
+    if (avatar_missing || avatar_force_update || SiteSetting.discourse_connect_overrides_avatar) && avatar_url.present?
       avatar_changed = sso_record.external_avatar_url != avatar_url
 
       if avatar_force_update || avatar_changed || avatar_missing
-        Jobs.enqueue(:download_avatar_from_url, url: avatar_url, user_id: user.id, override_gravatar: SiteSetting.sso_overrides_avatar)
+        Jobs.enqueue(:download_avatar_from_url, url: avatar_url, user_id: user.id, override_gravatar: SiteSetting.discourse_connect_overrides_avatar)
       end
     end
 
     if profile_background_url.present?
       profile_background_missing = user.user_profile.profile_background_upload.blank? || Upload.get_from_url(user.user_profile.profile_background_upload.url).blank?
 
-      if profile_background_missing || SiteSetting.sso_overrides_profile_background
+      if profile_background_missing || SiteSetting.discourse_connect_overrides_profile_background
         profile_background_changed = sso_record.external_profile_background_url != profile_background_url
         if profile_background_changed || profile_background_missing
           Jobs.enqueue(:download_profile_background_from_url,
@@ -322,7 +322,7 @@ class DiscourseSingleSignOn < SingleSignOn
 
     if card_background_url.present?
       card_background_missing = user.user_profile.card_background_upload.blank? || Upload.get_from_url(user.user_profile.card_background_upload.url).blank?
-      if card_background_missing || SiteSetting.sso_overrides_profile_background
+      if card_background_missing || SiteSetting.discourse_connect_overrides_profile_background
         card_background_changed = sso_record.external_card_background_url != card_background_url
         if card_background_changed || card_background_missing
           Jobs.enqueue(:download_profile_background_from_url,