Monitor Upstream Feature Flags

JH team will figure out a way to monitor feature flag changes from upstream.

discuss issue with upstream: https://gitlab.com/gitlab-jh/gitlab-jh-enablement/-/issues/179.

demo project https://jihulab.com/maochao-free-group/test-project/-/blob/main/.gitlab-ci.yml

use CI job to check whether feature flags changes, pseudo code:

1. only run on main-jh branch, allow_failure: true
2. get upstream_latest_commit from config/feature_flags
3. get JH_know_latest_commit from CI cache
4. check JH_know_latest_commit equal upstream_latest_commit or not
5. if equal, do nothing
6. if not equal
   1. send slack message to notify dev, https://api.slack.com/apps/A03G9B75PSS/incoming-webhooks
   2. create jihulab issue for tracking, https://docs.gitlab.com/ee/api/issues.html#new-issue
   3. save upstream_latest_commit as JH_know_latest_commit in CI cache