meta-app-framework: update Flutter app template

meta-app-framework: update Flutter app template

Update systemd template unit for Flutter based applications for the
embedder binary rename (to flutter-auto) and a required rename of the
application id command-line option (to --xdg-shell-app-id).

Bug-AGL: SPEC-4485

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: Icb03775f379929a852d3b270d52b3e88277aa3cc
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/27862
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
ci-image-boot-test: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Tested-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>