feat: implement version flags

This moves the version command to the dokku binary, and also implements both -v and --version flags on the binary.

plugins/00_dokku-standard/subcommands/version

@@ -1,12 +0,0 @@
-#!/usr/bin/env bash
-set -eo pipefail
-[[ $DOKKU_TRACE ]] && set -x
-source "$PLUGIN_CORE_AVAILABLE_PATH/common/functions"
-
-dokku_version_cmd() {
-  declare desc="prints dokku version"
-  local cmd="version"
-  cat "$DOKKU_ROOT/VERSION" || dokku_log_fail "Unable to determine dokku's version"
-}
-
-dokku_version_cmd "$@"