This is useful in contexts where the repository directory may be created and interacted with via git-http-backend or other methods of updating a repository.
- add `report` and `set` subcommands to the git plugin
- move configuring the DOKKU_DEPLOY_BRANCH to the git plugin
- implement configurable GIT_REV support
- migrate DOKKU_DEPLOY_BRANCH settings
- add a golang-compatible, shell based method of setting plugin configuration variables
Deprecates the community dokku-git-rev plugin.
Closes#2621
Refs dokku-community/dokku-git-rev#9
