Add delete_bot_comment command

What does this MR do and why?

In Feature Request: Ability to delete bot comments (#1537), while we are starting to add automated comment delete ability when certain processor's requirement is fulfilled, we would also like to give team member the ability to remove other bot comment, if the processor doesn't support automated deletion. For example the breaking change comment, it is only informational and doesn't necessarily require any resource update to satisfy any condition; we would still like to offer the resource owner the ability to remove this comment when it stops being useful.

Re: #1537

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