DEV: Rename secure_media to secure_uploads (#18376)

This commit renames all secure_media related settings to secure_uploads_* along with the associated functionality.

This is being done because "media" does not really cover it, we aren't just doing this for images and videos etc. but for all uploads in the site.

Additionally, in future we want to secure more types of uploads, and enable a kind of "mixed mode" where some uploads are secure and some are not, so keeping media in the name is just confusing.

This also keeps compatibility with the `secure-media-uploads` path, and changes new
secure URLs to be `secure-uploads`.

Deprecated settings:

* secure_media -> secure_uploads
* secure_media_allow_embed_images_in_emails -> secure_uploads_allow_embed_images_in_emails
* secure_media_max_email_embed_image_size_kb -> secure_uploads_max_email_embed_image_size_kb

spec/support/uploads_helpers.rb

@@ -13,9 +13,16 @@ module UploadsHelpers
     stub_request(:head, "https://#{SiteSetting.s3_upload_bucket}.s3.#{SiteSetting.s3_region}.amazonaws.com/")
   end
 
+  # TODO (martin) Remove this alias once discourse-chat plugin has been
+  # updated to use secure_uploads instead.
   def enable_secure_media
+    enable_secure_uploads
+    DiscourseEvent.trigger(:site_setting_changed, :secure_media, false, true)
+  end
+
+  def enable_secure_uploads
     setup_s3
-    SiteSetting.secure_media = true
+    SiteSetting.secure_uploads = true
   end
 
   def stub_upload(upload)