GitLab Pages - Storage size Limitations by Project or Group - backend

What does this MR do?

Backend implementation for #16610 (closed)

The columns were added in !17231 (merged) And closest_setting helper was added in !17769 (diffs)

The code is extracted to ee directory because we want to put it under GitLab Premium tier.

• Changelog is not added since frontend will be merged later.
• This MR also adds validations for max_pages/artifacts_size, which was forgotten earlier

Migration

Fixes application setting to match hard limit.

There is no need in reverting that operation, so there is only an empty down method.

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

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