refactor: combine both clone and sync commands

Using a single command will allow users to not have to worry about the workflow they use to setup or update a given app.

plugins/git/help-functions

@@ -28,8 +28,7 @@ fn-help-content() {
   declare desc="return help content"
   cat <<help_content
     git:allow-host <host>, Adds a host to known_hosts
-    git:clone [--build] <app> <repository> [<git-ref>], Creates an app from remote git repo
-    git:fetch [--build] <app> <repository> [<git-ref>], Fetch the app at an optional repo object and build the codebase
+    git:sync [--build] <app> <repository> [<git-ref>], Clone or fetch an app from remote git repo
     git:initialize <app>, Initialize a git repository for an app
     git:public-key, Outputs the dokku public deploy key
     git:report [<app>] [<flag>], Displays a git report for one or more apps