Add Rake task to show token expiration info

This task adds a Rake task `gitlab:tokens:analyze` and gives
a readout to the admin about:

- When the migration in 16.0 for
  https://gitlab.com/gitlab-org/gitlab/-/issues/369123 started and
  finished

- The top 10 expiration dates
  (https://gitlab.com/gitlab-org/gitlab/-/merge_requests/157782)
  https://gitlab.com/gitlab-org/gitlab/-/issues/467313

There should be a strong correlation with the migration dates and the
expiration dates. Seeing both of them together helps focus on the
tokens that were assigned an `expires_at` field in the background
migration.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/467313

Changelog: added

lib/tasks/gitlab/tokens.rake

+# frozen_string_literal: true
+
+module Tasks
+  module Gitlab
+    module Tokens
+      TOTAL_WIDTH = 70
+
+      class << self
+        def analyze
+          show_pat_expires_at_migration_status
+          show_most_common_pat_expiration_dates
+        end
+
+        def show_pat_expires_at_migration_status
+          sql = <<~SQL
+            SELECT * FROM batched_background_migrations
+            WHERE job_class_name = 'CleanupPersonalAccessTokensWithNilExpiresAt'
+          SQL
+
+          print_header("Personal Access Token Migration Status")
+
+          record = ApplicationRecord.connection.select_one(sql)
+
+          if record
+            puts "Started at: #{record['started_at']}"
+            puts "Finished  : #{record['finished_at']}"
+          else
+            puts "Status: Not run"
+          end
+
+          print_footer
+        end
+
+        def show_most_common_pat_expiration_dates
+          print_header "Top 10 Personal Access Token Expiration Dates"
+
+          puts "| Expiration Date | Count |"
+          puts "|-----------------|-------|"
+
+          PersonalAccessToken
+            .select(:expires_at, Arel.sql('count(*)'))
+            .where('expires_at >= NOW()')
+            .group(:expires_at)
+            .order(Arel.sql('count(*) DESC'))
+            .order(expires_at: :desc)
+            .limit(10)
+            .each do |row|
+            puts "| #{row[:expires_at].to_s.ljust(15)} | #{row[:count].to_s.ljust(5)} |"
+          end
+
+          print_footer
+        end
+
+        def print_header(title, total_width = TOTAL_WIDTH)
+          title_length = title.length
+          side_length = (total_width - title_length) / 2
+
+          left_side = "=" * side_length
+          right_side = "=" * (side_length + (total_width % 2))
+
+          header = "#{left_side} #{title} #{right_side}"
+          puts header
+        end
+
+        def print_footer
+          # Account for the spaces between the "=" in the header
+          puts "=" * (TOTAL_WIDTH + 2)
+        end
+      end
+    end
+  end
+end
+
+namespace :gitlab do
+  namespace :tokens do
+    desc 'GitLab | Tokens | Show information about tokens'
+    task analyze: :environment do |_t, _args|
+      Tasks::Gitlab::Tokens.analyze
+    end
+  end
+end