feat: flesh out git plugin further

- 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

plugins/git/post-delete

@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
+source "$PLUGIN_CORE_AVAILABLE_PATH/common/property-functions"
+
+trigger-git-post-delete() {
+  declare desc="destroys the git properties for a given app"
+  declare APP="$1"
+  fn-plugin-property-destroy "git" "$APP"
+}
+
+trigger-git-post-delete "$@"