Add bug::availability label when labeled with availability::limit

What does this MR do and why?

Related to #1025 (closed). Automatically add label bug::availability when an issue is labeled with availablity::limit

Result of MR

Closes #1025 (closed).

Applying the availability::limit label to an issue will result in:

1. bug::availability label applied
2. type::bug applied due to the previous reaction.

If type::bug is already applied to an issue, adding availability::limit will only result in the first reaction and will NOT impact the existing type::bug label.

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-with-a-dry-run on how to perform dry-runs.

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