Place Group by OWASP 2021 item behind a feature flag

Why are we doing this work

As discussed at &10164 (comment 1732113156), we have a very limited set of OWASP Top 10 2021 records at the moment. To avoid a confusing user experience, we should put 2021 behind a feature flag for now, additionally waiting for Include OWASP 2021 mapping to sast-rules (#438561 - closed) (groupstatic analysis) to progress.

Relevant links

Non-functional requirements

• Documentation:
• Feature flag:
• Performance:
• Testing:

Implementation plan

1. Create a feature flag
2. Similar to https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/app/assets/javascripts/security_dashboard/components/shared/vulnerability_report/vulnerability_report.vue#L185, add another clause for 2021 OWASP that puts it behind the feature flag.

Verification steps

1. Go to https://gitlab.com/gitlab-org/govern/threat-insights-demos/verification-projects/verify-epic-10164/-/security/vulnerability_report (ff disabled)
2. Verify that OWASP 2021 is not displayed in Group By options
3. Go to https://gitlab.com/gitlab-org/govern/threat-insights-demos/verification-projects/verify-issue-438788/-/security/vulnerability_report (ff enabled)
4. Verify that OWASP 2021 is displayed in the Group By options