Encourage create new cops in gitlab-styles repository

What does this MR do?

This MR highlights in the "New Static Analysis" MR template that new 👮 should go to GitLab Styles as already stated in our contribution documentation.

Thanks to @dstull for pointing this out after I've created !53486 (closed).

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