Allows any user to comment on a dismissed vulnerability (Dismissal reason: Step 3)

What does this MR do?

This adds in the frontend work for allowing any user to provide a reason for vulnerability dismissal. It also allows the addition of a dismissal reason after a vulnerability has been dismissed. Previously you could only add a reason at the time of the dismissal.

This is dependant on the backend work in !11963 (merged)

See this video for how to set up your local environment to test this MR 🎧 : dismissal_comment_part_1

See this video for a walkthrough of what it all looks like 🎧 : dismissal_comment_part_2

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

Closes #10364 (closed)