Refactor the Deployment model so state machine events are used by both CI and the API
What does this MR do?
This refactors Deployment, Deployments::CreateService, and
Deployments::UpdateService so that the appopriate state machine events
are triggered when creating or updating a deployment. Without this we
would not trigger any events when creating deployments using the API,
such as the event used for setting finished_at.
As part of this change, Deployments::CreateService no longer calls Deployments::AfterCreateService directly; instead it uses Sidekiq which is triggered using a state machine event.
This ensures that deployments created using the API and CI both trigger the same workers, hooks, etc.
To make this work some specs had to be adjusted, which included adjusting some Gitaly request count limits that were racy.
This fixes #36648 (closed) and fixes #35763 (closed).