Add more instance stats APIs (#6125)

* Add GET /api/v1/instance/peers API to reveal known domains

* Add GET /api/v1/instance/activity API

* Make new APIs disableable, exclude private statuses from activity stats

* Fix code style issue

* Fix week timestamps

app/models/status.rb

@@ -135,6 +135,7 @@ class Status < ApplicationRecord
   end
 
   after_create_commit :store_uri, if: :local?
+  after_create_commit :update_statistics, if: :local?
 
   around_create Mastodon::Snowflake::Callbacks
 
@@ -308,4 +309,9 @@ class Status < ApplicationRecord
   def set_local
     self.local = account.local?
   end
+
+  def update_statistics
+    return unless public_visibility? || unlisted_visibility?
+    ActivityTracker.increment('activity:statuses:local')
+  end
 end