Adds a popover to vulnerability-check approvals

What does this MR do?

This adds the frontend component to #9928 (closed)

It simply adds a popover helper to explain the use of the Vulnerability-Check group.

There's a couple of bits missing on this, but we can add them in later.

1. The link to the documentation is missing because I don't think the docs exist for it yet.
2. There's a couple of UI discrepancies, but I've explained them in this handy video:

approval_popover

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Performance 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