Self-monitoring docs deprecation warnings

doc/administration/monitoring/gitlab_self_monitoring_project/index.md

@@ -4,10 +4,15 @@ group: Respond
 info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
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-# Self-monitoring project **(FREE SELF)**
+# Self-monitoring project (DEPRECATED) **(FREE SELF)**
 
 > - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/32351) in GitLab 12.7 [with a flag](../../feature_flags.md) named `self_monitoring_project`. Disabled by default.
 > - Generally available in GitLab 12.8. [Feature flag `self_monitoring_project`](https://gitlab.com/gitlab-org/gitlab/-/issues/198511) removed.
+> - [Deprecated](https://gitlab.com/gitlab-org/gitlab/-/issues/348909) in GitLab 14.9. Planned for removal in GitLab 15.0.
+
+WARNING:
+This feature is in its end-of-life process. It is [deprecated](https://gitlab.com/gitlab-org/gitlab/-/issues/348909)
+for use in GitLab 14.9, and is planned for removal in GitLab 15.0.
 
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