Create CI pipeline to apply Helm release for executing Container Registry post deployment migrations

Problem statement

Post deployment migrations (PDMs) for the Container Registry metadata database on production, staging and preprod are currently executed manually. In this epic (gitlab-org&17933), we are automating the execution of PDMs for Container Registry.

We need to create a CI pipeline for applying the Helm release created in #21258 (closed).

Proposal

• The CI pipeline should execute PDMs on pre and staging first, and then in production.
• Execution of PDMs in each environment should be done in a child pipeline, allowing the trigger job to use a resource_group that will serve as a "pipeline lock". In addition, the job in the child pipeline that actually applies changes to the cluster can use the cluster level resource_group. Opened #21504
• Send notifications to #announcements and #g_container-registry channels in Slack Opened #21505.
• To prevent auto-deploy packages being deployed at the same time, execution of the new pipeline for Container Registry PDMs will have to be coordinated with Release Managers.