Post a comment to the monthly issue when coordinated pipeline starts

What does this MR do?

1. Add class AutoDeploy::CoordinatedPipeline::PostDeployMigrations::Files to list post deployment migration filepaths.
2. Add class Tasks::AutoDeploy::StartNote to create a note in the monthly issue.
3. Create a rake task to call Tasks::AutoDeploy::StartNote called auto_deploy:post_start_note.
4. Call the auto_deploy:post_start_note rake task in the metrics:start_time job, which runs after the wait:helm and wait:omnibus jobs.

gitlab-com/gl-infra/delivery#2224 (closed)

Author Check-list

• [-] Has documentation been updated?