FIX: Further improvements for plugin list (#24622)

Followup e37fb3042d

* 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.

lib/plugin/metadata.rb

@@ -111,10 +111,28 @@ class Plugin::Metadata
     required_version
     transpile_js
     meta_topic_id
-    experimental
+    label
   ]
   attr_accessor(*FIELDS)
 
+  MAX_FIELD_LENGTHS ||= {
+    name: 75,
+    about: 350,
+    authors: 200,
+    contact_emails: 200,
+    url: 500,
+    label: 20,
+  }
+
+  def meta_topic_id=(value)
+    @meta_topic_id =
+      begin
+        Integer(value)
+      rescue StandardError
+        nil
+      end
+  end
+
   def self.parse(text)
     metadata = self.new
     text.each_line { |line| break unless metadata.parse_line(line) }
@@ -130,12 +148,17 @@ class Plugin::Metadata
 
     unless line.empty?
       return false unless line[0] == "#"
-      attribute, *description = line[1..-1].split(":")
+      attribute, *value = line[1..-1].split(":")
 
-      description = description.join(":")
+      value = value.join(":")
       attribute = attribute.strip.gsub(/ /, "_").to_sym
 
-      self.public_send("#{attribute}=", description.strip) if FIELDS.include?(attribute)
+      if FIELDS.include?(attribute)
+        self.public_send(
+          "#{attribute}=",
+          value.strip.truncate(MAX_FIELD_LENGTHS[attribute] || 1000),
+        )
+      end
     end
 
     true