Fixes post-deploy pipeline notifications and dependencies

What does this MR do and why?

The post-migrations notifications are shared across the coordinated pipeline and the post-deploy pipeline. During the post-deploy pipeline testing, it was noted the post-migrations jobs are named differently on each pipeline which caused the notifications to failed during the testing.

This commit fixes the PostDeployMigrations::Notifier class to consider different naming based on the pipeline. This is a bit hack-ish, but it should be cleaned once the post-deploy pipeline is used and the post-migrations on the coordinated pipeline are deprecated (follow-up issue gitlab-com/gl-infra/delivery#2354 (closed))

This commit also establishes dependencies:

• It makes the tracking_success and tracking_failed to depend on the tracking_running job, this prevents from both jobs to run at the same time
• It makes the notify_failure and notify_success job to depend on the notify_start job in case the migrations are executed failure quickly.

Related to gitlab-com/gl-infra/delivery#2352 (closed)

Author Check-list

• [-] Has documentation been updated?