Draft: Add gitlab-styles/rubocop

What does this MR do?

Add Rubocop to triage-ops 🎉.

Specifically,

• Dogfoods gitlab-styles
• Adds a rubocop job in the CI
• Adds a .rubocop_todo.yml for the not-yet-fixed rubocop offenses.
• We went from ~900 offenses to < 150 🎉
• Adds rubocop to lefthook

Expected impact & dry-runs

All specs are passing: no impact expected.

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