More verbose logging for deprecated path access

Current logging tells us we've isolated the calls to about 5 call sites,
now we'd like to know what is calling these methods.

config/initializers/deprecations.rb

-deprecator = ActiveSupport::Deprecation.new('11.0', 'GitLab')
-
 if Gitlab.dev_env_or_com?
+  deprecator = ActiveSupport::Deprecation.new('11.0', 'GitLab')
+
+  deprecator.behavior = -> (message, callstack) {
+    Rails.logger.warn("#{message}: #{callstack[1..20].join}")
+  }
+
   ActiveSupport::Deprecation.deprecate_methods(Gitlab::GitalyClient::StorageSettings, :legacy_disk_path, deprecator: deprecator)
 end