Update artifact size authorization

What does this MR do?

This is part of the work for #21688 (closed). This covers updating the authorization logic for artifacts size to now factor in the new project and namespace level max_artifacts_size setting.

This also adds a new helper method Project#closest_setting which fetches the closest non-nil value for a given setting name. This will be useful for other settings like max_pages_size.

A separate MR will be opened for implementing the form fields for these new settings.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance 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