Add users allow-list to git abuse rate limit settings (UI)

What does this MR do and why?

Resolves https://gitlab.com/gitlab-org/modelops/anti-abuse/team-tasks/-/issues/17

1. Create Vue form to let admins configure git abuse rate limits -> Number of Repositories, Reporting Time Period & Excluded Users (i.e. users allow-list)

2. Since, the users allow-list is a dynamic component, this MR also refactors the existing form from HAML to Vue. Subsequently, feature specs + view specs are updated.

Screenshots or screen recordings

allowlist

How to set up and validate locally

1. Enable the feature flag git_abuse_rate_limit_feature_flag & ensure you are on the Ultimate license

bundle exec rails c
> Feature.enable(:git_abuse_rate_limit_feature_flag)

2. Sign in as admin
3. Navigate to http://localhost:3000/admin/application_settings/reporting

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

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