FIX: Further improvements for plugin list (#24622)

Followup e37fb3042d6f56a27a01614e57bc7029f472b0c9

* Automatically remove the prefix `Discourse ` from all the plugin titles to avoid repetition
* Remove the :discourse_dev: icon from the author. Consider a "By Discourse" with no labels as official
* We add a `label` metadata to plugin.rb
  * Only plugins made by us in `discourse` and `discourse-org` GitHub organizations will show these in the list
* Make the plugin author font size a little smaller
* Make the commit sha look like a link so it's more obvious it goes to the code

Also I added some validation and truncation for plugin metadata
parsing since currently you can put absolutely anything in there
and it will show on the plugin list.

app/serializers/admin_plugin_serializer.rb

@@ -11,8 +11,8 @@ class AdminPluginSerializer < ApplicationSerializer
              :enabled_setting,
              :has_settings,
              :is_official,
-             :is_experimental,
              :is_discourse_owned,
+             :label,
              :commit_hash,
              :commit_url,
              :meta_url,
@@ -79,8 +79,13 @@ class AdminPluginSerializer < ApplicationSerializer
     Plugin::Metadata::OFFICIAL_PLUGINS.include?(object.name)
   end
 
-  def is_experimental
-    object.metadata.experimental
+  def include_label?
+    is_discourse_owned
+  end
+
+  def label
+    return if !is_discourse_owned
+    object.metadata.label
   end
 
   def is_discourse_owned