Add git anti-abuse settings for self-managed instances

What does this MR do and why?

• Adds git anti-abuse rate limits which can be configured by admins.
• These settings are only available for self-managed instances on the Ultimate plan.
• Makes sure that these settings don't get returned as part of the GET application/settings API endpoint since we wouldn't want anti-abuse settings to be exposed.

Screenshots or screen recordings

How to set up and validate locally

1. Enable the feature flag git_abuse_rate_limit_feature_flag: echo "Feature.enable(:git_abuse_rate_limit_feature_flag)" | rails c
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.

Resolves modelops/anti-abuse/team-tasks/-/issues/12