Aligns the autodevops banner with the gl-ui banner

What does this MR do?

This MR aligns the autodevops banner with the banner component in gitlab ui.

It fixes some issues with spacing, borders, etc.

It's still WIP as we need the correct illustration added to GitLab SVGs gitlab-svgs!504 (merged)

Screenshots

Before	After

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