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/assets/javascripts/admin/addon/controllers/admin-user-index.js

@@ -590,7 +590,7 @@ export default Controller.extend(CanCheckEmails, {
 
     deleteSSORecord() {
       return bootbox.confirm(
-        I18n.t("admin.user.sso.confirm_delete"),
+        I18n.t("admin.user.discourse_connect.confirm_delete"),
         I18n.t("no_value"),
         I18n.t("yes_value"),
         (confirmed) => {

app/assets/javascripts/admin/addon/templates/user-index.hbs

@@ -70,8 +70,8 @@
         {{/if}}
       </div>
       <div class="controls">
-        {{#if siteSettings.sso_overrides_email}}
-          {{i18n "user.email.sso_override_instructions"}}
+        {{#if siteSettings.auth_overrides_email}}
+          {{i18n "user.email.auth_override_instructions"}}
         {{else if model.email}}
           {{html-safe (i18n "admin.user.visit_profile" url=preferencesPath)}}
         {{/if}}
@@ -105,8 +105,8 @@
       <div class="controls">
         {{#if model.email}}
           {{#if model.secondary_emails}}
-            {{#if siteSettings.sso_overrides_email}}
-              {{i18n "user.email.sso_override_instructions"}}
+            {{#if siteSettings.auth_overrides_email}}
+              {{i18n "user.email.auth_override_instructions"}}
             {{else}}
               {{html-safe (i18n "admin.user.visit_profile" url=preferencesPath)}}
             {{/if}}
@@ -646,11 +646,11 @@
 
 {{#if model.single_sign_on_record}}
   <section class="details">
-    <h1>{{i18n "admin.user.sso.title"}}</h1>
+    <h1>{{i18n "admin.user.discourse_connect.title"}}</h1>
 
     {{#with model.single_sign_on_record as |sso|}}
       <div class="display-row">
-        <div class="field">{{i18n "admin.user.sso.external_id"}}</div>
+        <div class="field">{{i18n "admin.user.discourse_connect.external_id"}}</div>
         <div class="value">{{sso.external_id}}</div>
         {{#if model.can_delete_sso_record}}
           <div class="controls">
@@ -658,22 +658,22 @@
               class="btn-danger"
               action=(action "deleteSSORecord")
               icon="far-trash-alt"
-              label="admin.user.sso.delete_sso_record"
+              label="admin.user.discourse_connect.delete_sso_record"
             }}
           </div>
         {{/if}}
       </div>
       <div class="display-row">
-        <div class="field">{{i18n "admin.user.sso.external_username"}}</div>
+        <div class="field">{{i18n "admin.user.discourse_connect.external_username"}}</div>
         <div class="value">{{sso.external_username}}</div>
       </div>
       <div class="display-row">
-        <div class="field">{{i18n "admin.user.sso.external_name"}}</div>
+        <div class="field">{{i18n "admin.user.discourse_connect.external_name"}}</div>
         <div class="value">{{sso.external_name}}</div>
       </div>
       {{#if canAdminCheckEmails}}
         <div class="display-row">
-          <div class="field">{{i18n "admin.user.sso.external_email"}}</div>
+          <div class="field">{{i18n "admin.user.discourse_connect.external_email"}}</div>
           {{#if ssoExternalEmail}}
             <div class="value">{{ssoExternalEmail}}</div>
           {{else}}
@@ -687,12 +687,12 @@
         </div>
       {{/if}}
       <div class="display-row">
-        <div class="field">{{i18n "admin.user.sso.external_avatar_url"}}</div>
+        <div class="field">{{i18n "admin.user.discourse_connect.external_avatar_url"}}</div>
         <div class="value">{{sso.external_avatar_url}}</div>
       </div>
       {{#if sso.last_payload}}
         <div class="display-row">
-          <div class="field">{{i18n "admin.user.sso.last_payload"}}</div>
+          <div class="field">{{i18n "admin.user.discourse_connect.last_payload"}}</div>
           <div class="value">
             {{#each ssoPayload as |line|}}
               {{line}}<br>