Refine the guidance users are given in the pipeline editor when trying to enable DAST or API Fuzzing

UX Scorecard recommendation from: gitlab-design#1829

Problem to solve

When enabling DAST or API fuzzing through the UI, it's isn't obvious how and where to insert the code snippet into the gitlab-ci.yml file. The banner at the top of the pipeline editor page attempts to address this but could be refined to improve clarity. Note that the banner is the same for DAST and API Fuzzing

Improvements to the snippet comments could be considered as well.

Proposal

Explore how we might refine the guidance users are given in the pipeline editor when trying to enable DAST so that the required actions are more clear.