Measure coordinated deployment duration

What does this MR do?

Measure the deployment duration time in seconds from the staging to the production deployment. Adds two new stages to the coordinated pipeline:

• coordinated:metrics:prepare triggers a job that registers the coordinated deployment start time. It's executed after the build stage and before the deployment to staging starts.
• coordinated:finish triggers a job that uses the deploy start time to calculate the deployment duration. It also sends the difference to Prometheus PushGateway

Implementation is behind a feature flag

As part of gitlab-com/gl-infra/delivery#1698 (closed)

Author Check-list

• [-] Has documentation been updated?