Instrument `RepositoryCheck::SingleRepositoryWorker` manually

This worker is called manually by `RepositoryCheck::BatchWorker` meaning it's not tracked automatically by the Sidekiq middleware.

CHANGELOG

@@ -41,6 +41,7 @@ v 8.9.0 (unreleased)
   - Put project Files and Commits tabs under Code tab
   - Replace Colorize with Rainbow for coloring console output in Rake tasks.
   - An indicator is now displayed at the top of the comment field for confidential issues.
+  - RepositoryCheck::SingleRepositoryWorker public and private methods are now instrumented
 
 v 8.8.4 (unreleased)
   - Ensure branch cleanup regardless of whether the GitHub import process succeeds

config/initializers/metrics.rb

@@ -121,6 +121,13 @@ if Gitlab::Metrics.enabled?
     config.instrument_instance_methods(Gitlab::GitAccessWiki)
 
     config.instrument_instance_methods(API::Helpers)
+
+    config.instrument_instance_methods(RepositoryCheck::SingleRepositoryWorker)
+    # Iterate over each non-super private instance method to keep up to date if
+    # internals change
+    RepositoryCheck::SingleRepositoryWorker.private_instance_methods(false).each do |method|
+      config.instrument_instance_method(RepositoryCheck::SingleRepositoryWorker, method)
+    end
   end
 
   GC::Profiler.enable