Process security report observability events

What does this MR do and why?

• Feature is behind a feature flag :process_scan_events
• Add a new sidekiq worker to process observability events included in security reports.
• Add events included in security reports via the internal events api
• Only process event names listed in allow list
• Tests

References

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• Update security report processing to handle met... (#473109 - closed) • Michael Eddington • 17.10

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Before	After

How to set up and validate locally

Testing this feature is done by submitting a security report via a pipeline job that contains an observability section. This MR contains two security reports that can be used to perform local validation:

• ee/spec/fixtures/security_reports/master/gl-dast-report-observability.json -- This report contains an even that is allowed by the allow list. The expected behavior is an exception (Gitlab::Tracking::EventValidator::UnknownEventError) from the internal events api because the event is not registered. However, this proves we are calling the internal events API correctly.
• ee/spec/fixtures/security_reports/master/gl-dast-report-observability-unknown-event.json -- This report contains an event that is not allowed by the allow list. This will result in an exception Security::ProcessScanEventsService::ScanEventNotInAllowListError. This shows the allow list logic is working correctly.

NOTE: This feature is behind a feature flag, don't forget to enable the feature for the project uploading the report.

1. Create a new project
2. Enable FF (process_scan_events) for this new project
3. Add security report(s) to project repository
4. Add a .gitlab-ci.yml file with the following contents (replacing SECURITY_REPORT_FILE_NAME_HERE):

dast:
  stage: test
  script:
    - echo "Hello world!"
  artifacts:
    when: always
    reports:
      dast: SECURITY_REPORT_FILE_NAME_HERE

1. Run the pipeline
2. Check the logs based on expected result from the report used (see reports above)

Related to #473109 (closed)