Rolling deployments for repo updates

[jvstme]

• Support rolling deployments for services when
  the run repo is updated: new commits are added,
  the branch is changed, uncommitted files are
  updated, etc. Switching from one repo to another
  is not yet supported.

  Note: A side effect of this change is that
  if the run configuration file is stored in the
  same repo that is used for the run, any changes
  to the configuration file will also be
  considered a change to the repo
  (repo_code_hash), and hence require a rolling
  deployment for services or a full restart for
  tasks and dev environments. Previously, this was
  not the case, since changes to repo_code_hash
  were ignored for existing jobs. This new
  behavior makes it more difficult to avoid
  redeployment when changing some configuration
  properties, namely priority,
  inactivity_duration, replicas, and
  scaling. However, we consider this acceptable,
  since changing these properties in-place is an
  advanced use case and can still be achieved by
  moving the configuration file out of the repo.

• Improve run plan output in dstack apply when
  attempting an in-place update:

  • Show not only the list of changed
    configuration properties, but also other
    changes from the run spec, such as
    repo-related changes.

    $ dstack apply -f test-service.dstack.yml
    
    Active run test-service already exists. Detected changes that can be updated in-place:
    - Repo state (branch, commit, or other)
    - Repo files
    - Configuration properties:
      - env
    
    Update the run? [y/n]:

  • Show the list of changes not only when
    in-place update is possible, but also when it
    is not. This will help users understand why a
    run cannot be updated in-place.

    $ dstack apply -f test-service.dstack.yml
    
    Active run test-service already exists. Detected changes that cannot be updated in-place:
    - Repo files
    - Configuration properties:
      - gateway
    
    Stop and override the run? [y/n]:

    Currently, all detected changes are listed
    together. An area for future improvement is
    highlighting the changes that prevent an
    in-place update.

#2180