Simplify broken master incident template

What does this MR do and why?

Closes Simplify master-broken incident issue description (gitlab-org/quality/engineering-productivity/team#313 - closed).

It has been suggested that the broken master incident issue has become too long to attract engagement. It's time to de-clutter the description and make it crystal clear what we need to do to close the incident.

Before/After screenshots:

before:

Click to expand

after:

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