Add "Activity" column to pipeline security report

Summary

In order to display a finding's related issue we need to add a column (named "Activity") to the report. This is following what we display on the vulnerability report:

vulnerability report

Implementation steps

1. Add FIELDS.ACTIVITY in ee/app/assets/javascripts/security_dashboard/components/pipeline/pipeline_vulnerability_report.vue
2. Update specs accordingly

Verification steps

1. Go to https://gitlab.com/gitlab-org/govern/threat-insights-demos/verification-projects/security-reports-pipeline-security-listing-migration-and-enhancements/-/pipelines/1100011493/security
2. Verify there is an activity column. Except for a false-positive badge, it will be empty. No related issues are shown yet. That is coming with Show related issues on pipeline security tab (#433477 - closed) • David Pisek, Lorenz van Herwaarden • 16.7