Add automated protection for tech_stack.yml modifications

What does this MR do and why?

Describe in detail what your merge request does and why.

This MR implements an automated policy to protect tech_stack.yml from unauthorized modifications and guide contributors through the new HelpLab process.

Changes

• Added policies/tech-stack-protection.yml - triage-ops policy to detect tech_stack.yml changes
• Added run_tech_stack_policy job in .gitlab-ci.yml - runs the policy on all merge requests

• /policies/tech-stack-protection.yml
• /.gitlab-ci.yml

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