Limit page number on explore/projects

What does this MR do?

Prevents browsing to high page numbers on explore/projects. Realistically you'd have to be extremely bored as a human to browse that far, but crawlers will hit them. These pages are very slow due to a combination of two issues (a slow query, multiplied by OFFSET pagination slowness), so pending changes to resolve the underlying issue, this MR takes a simple step of blocking pages after a certain point.

I've implemented the limiter as a generic controller concern, partly for neatness but also as it could be easily implemented in other areas of the application later if we find similar issues elsewhere.

WIP at the moment because the actual messaging most likely needs to come from someone else.

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

Related #36749 (closed)