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 https://gitlab.com/gitlab-org/gitlab/issues/36648 and fixes
https://gitlab.com/gitlab-org/gitlab/issues/35763.
Co-Authored-By: Alessio Caiazza <acaiazza@gitlab.com>