feat: add git:auth-status to check netrc match

Adds `git:auth-status HOST [USERNAME] [PASSWORD]` which exits 0 when the
configured `.netrc` entry matches the requested state and 1 otherwise,
allowing external tooling to detect whether `git:auth` would change
anything without reading `$DOKKU_ROOT/.netrc` directly. Both `git:auth`
and `git:auth-status` now also accept the password via `STDIN`.

plugins/git/subcommands/auth-status

@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+source "$PLUGIN_AVAILABLE_PATH/git/internal-functions"
+set -eo pipefail
+[[ $DOKKU_TRACE ]] && set -x
+
+cmd-git-auth-status "$@"