Add local followers page to admin account UI (#9610)

* Add local followers page to admin account UI

For moderation, I often find myself wondering who, locally, is following
a remote user. Currently, to see this, I have to go back to the web UI,
paste in their full handle, click their profile, and go to the
"Followers" tab (plus, this information is incidental, and if mastodon
ever decides to resolve all of the follower information, there will be
no place local followers are shown). This PR adds a new page which is
accessible via the "following" count on the admin's account view
page, which shows the local followers. (It has filter parameters for
account location to indicate that only local followers are shown, and
leave room for expansion if mastodon ever decides to store the entire
remote follow list).

* Normalize en.yml

app/models/account.rb

@@ -139,6 +139,10 @@ class Account < ApplicationRecord
     "#{username}@#{Rails.configuration.x.local_domain}"
   end
 
+  def local_followers_count
+    Follow.where(target_account_id: id).count
+  end
+
   def to_webfinger_s
     "acct:#{local_username_and_domain}"
   end