Code Quality template: Add support for Merge Request pipelines

What does this MR do?

Currently, the Code Quality template only supports the Branch-Pipelines template.

To also support Merge Request pipelines, the only missing scenario is a rule that triggers the job when the CI_MERGE_REQUEST_IID variable is set.

Conformity

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