Add pipeline statuses subscription

What does this MR do and why?

Adds ci_pipeline_statuses_updated subscription to provide real-time updates to the UI. A user subscribes to a project and when a pipeline updates that pipeline is sent to the client. Follows a very similar pattern that I did for pipeline schedules as seen here: !200990 (merged)

This is a key feature needed to support real-time statuses on Build > Pipelines and an MR pipelines tab.

References

Screenshots or screen recordings

How to set up and validate locally

1. Enable FF ci_pipeline_statuses_updated_subscription
2. Create a pipeline (or multiple to help with testing)
3. Visit http://gdk.test:3000/-/graphql-explorer and use the subscription with your project ID (where the pipelines are)

subscription {
  ciPipelineStatusesUpdated(projectId: "gid://gitlab/Project/19") {
    id
    status 
  }
}

4. Trigger a change on the pipeline and watch data update in the explorer and network tab (sockets)

OR trigger pipeline changes in rails console based on and ID

pipeline = Ci::Pipeline.find(YOUR_ID)

# Test multiple status changes

pipeline.run!
# Check subscription fired with "running"

pipeline.succeed!
# Check subscription fired with "success"

pipeline.run!
# Check subscription fired again with "running"

pipeline.drop!
# Check subscription fired with "failed"

MR acceptance checklist

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