Add namespace size checker

What does this MR do?

Part of: https://gitlab.com/gitlab-org/gitlab/-/issues/211859 Issue: #214790 (closed)

Adds a namespace storage size checker that we can use for the following use-cases to warn users that their storage is on the limit in follow-up MRs:

1. For git push in PostReceiveService
2. For alert banners on the Project and Group page of a namespace
3. In a Job after RootStatisticWorker gets executed to check if the namespace should be set to read-only
4. In the Web IDE to alert users when the capacity exceeded.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team