allow users to specify the fork by adding a fork attribute to the changeset template with the following possibilities as shown in to Adam's prior example below

changesetTemplate:
  fork: foo           # forks into the `foo` organisation/user, assuming the
                      # user has permission
  fork: LawnGnome     # forks into the user's namespace as well (assuming the
                      # user is LawnGnome), but explicitly by name
  fork: user          # forks into the user's namespace, same as the current

With fork being a string pointing to the owner to fork into, with user being the current user. This is to address permissions errors faced when attempting to creat forks in non accessible repos

tracked by #33110