Introduce PlanLimitChange for limit tracking

What does this MR do and why?

#1 MR relates to: https://gitlab.com/gitlab-org/gitlab/-/issues/395530

In this MR:

We are Introducing plan_limit_changes table and PlanLimitChange model

This will allow us to:

• Track the changes that happen to enforcement_limit, notification_limit, storage_size_limit columns.
• Build the logic needed to have this design in later steps.

Note: Initially, we planned to use AuditEvents to track these changes, but this might not be the best approach for how they need to be exposed

• See "changelog" section

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.