[MR Widget V2] Add dismissed label to findings when they are dismissed

Summary

Add the dismissed label to findings when a finding is already dismissed.

Screenshots

Implementation plan

• Update https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/app/assets/javascripts/vue_merge_request_widget/extensions/security_reports/mr_widget_security_reports.vue to show the dismissed label.

Verification steps

• Follow the steps to enable this feature locally: !104100 (merged). If you use Mokku, you can use the exported file to produce mock data, otherwise you'll have to create findings and dismiss one of them. The tested version does not allow dismissing vulnerabilities, so you may have to turn off the feature flag, dismiss a vulnerability and then re-enable the feature flag.
• Check the dismissed label is there