Over limit members in namespaces with a free plan

What does this MR do and why?

Draft: Detect members over limit in namespaces with a free plan. Rate members for a root level namespace

• Followup MR will consume Namespace#memberships_to_be_deactivated method Background job to trim namespaces which are ove... (!82791 - closed)
• All database, scaling estimations and work are done in Background job to trim namespaces which are ove... (!82791 - closed)
• Verify bots and whether they stay in/out etc

Related to #347447+ and #349813+

How to set up and validate locally

• Simulate SaaS(Gitlab.com)
• • On rails console run

  namespace.memberships_to_be_deactivated
  group..memberships_to_be_deactivated

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.