Add RecordCountMonitor warning

What does this MR do and why?

This MR introduces a new class RecordCountMonitor to warn in development when more than 1_000 records are loaded in memory.

It gets rid of the following warning 👇

DEPRECATION WARNING: `config.active_record.warn_on_records_fetched_greater_than` is deprecated and will be removed in Rails 8.0. Please subscribe to `sql.active_record` notifications and access the row count field to detect large result set sizes. (called from <main> at /Users/morefice/code/gitlab-development-kit/gitlab/config/environment.rb:7)