Frontend - Resolve "Display in MR if security report is outdated"

What does this MR do?

Fixes Issue #4913 (closed)

When the last pipeline for the target branch hadn't detected some security issues, maybe due to jobs failed or artifacts expired, the MR security report should be considered outdated and the pipeline needs to be re-run. It also handles the edge case when target branch has received more commits and the current branch needs to be updated.

Backend branch for this feature has been merged - !21220 (merged)

Screenshots

Ideal Experience

When MR branch is outdated

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