Use gl-drawer for pipeline editor help drawer

What does this MR do and why?

For #348523 (closed)

This replaces the implementation of the pipeline drawer with gl-drawer so that the styling and behavior is aligned with GitLab's design.

The drawer can now be opened using the Help button in the editor.

Screenshots or screen recordings

Before	After
before	after

How to set up and validate locally

1. Visit the Pipeline Editor (CI/CD > Editor)
2. Click on the Help button to open the drawer.
3. Verify the changes.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.