Identify duplicate incident

What does this MR do and why?

Re: gitlab-org/gitlab#395280 (closed)

Allow @gitlab-bot to help us identify if a new incident duplicates a previous one. This is achieved with the following steps:

1. Before a new incident is created, it will fetch the last incident that was previously created, and compare the job names
2. If the soon-to-be created incident has the same failed jobs as the previous incident, AND if the previous incident was marked as a duplicate of an earlier incident, then this new incident has a high chance to be a duplicate as well
3. As a result, the current incident will have the following comment to the Investigation Steps discussion

Identified as a duplicate of incident 1.

/copy_metadata #1
/duplicate #1

Closes gitlab-org/gitlab#395280 (closed)

Expected impact & dry-runs

These are strongly recommended to assist reviewers and reduce the time to merge your change.

See https://gitlab.com/gitlab-org/quality/triage-ops/-/tree/master/doc/scheduled#testing-policies-with-a-dry-run on how to perform dry-runs for new policies.

See https://gitlab.com/gitlab-org/quality/triage-ops/-/blob/master/doc/reactive/best_practices.md#use-the-sandbox-to-test-new-processors on how to make sure a new processor can be tested.

Action items

• If adding environment variables for reactive processors, update config/triage-web.yaml and .gitlab/ci/triage-web.yml
• (If applicable) Add documentation to the handbook pages for Triage Operations =>
• (If applicable) Identify the affected groups and how to communicate to them:
  • /cc @person_or_group =>
  • Relevant Slack channels =>
  • Engineering week-in-review