Moving gitlab_loose_foreign_keys.yml to config/

What does this MR do and why?

This MR addresses issue #350090 (closed)

How I tested it?

Gitlab::Database::LooseForeignKeys.send(:loose_foreign_keys_yaml)

gives still gives the expected parsed YAML response

Gitlab::Database::LooseForeignKeys.loose_foreign_keys_yaml_path
=> #<Pathname:/home/omar/gitlab/gitlab-development-kit/gitlab/config/gitlab_loose_foreign_keys.yml>

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.

Related to #350090 (closed)