Fedramp reactive automation

What does this MR do and why?

Iteration 1 described in https://gitlab.com/gitlab-org/quality/triage-ops/-/issues/1088#note_1086012523.

Reactive automation for setting expectation of FedRAMP vulnerability SLO when it first encounters a fedRAMP vulnerability issue.

Closes https://gitlab.com/gitlab-org/quality/triage-ops/-/issues/1088

Expected impact & dry-runs

This processor reacts to issue.open and issue.update events, checks for the following conditions:

• event is emitted from gitlab-org
• event involves label changes (both add and remove)
• vulnerability label is present (either ~"FedRAMP Milestone::Vuln Remediation" or ~"Vulnerability SLA")
• severity label is present (severity1, severity2, severity3, severity4)
• if the issue has no previous unique comment for the specific SLO target (we do not want to repeat the reminder if the same SLO applies after label change)

Action items

• (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