Docker image for Shopware 6.5

Hey, Since Shopware 6.5 extensions are allowed to run `composer` while installation. This will change on runtime the vendor folder so the current docker image cannot be used in a cluster system or with Shopware updates anymore. The new image is just a base image containing PHP + Webserver. The Dockerfile in your project should build Shopware with your extensions and copy it into `/var/www/html`. In this way we can work again with cluster/multiple same containers. I have created an example project [here](https://github.com/shyim/shopware/tree/main/example-project) and looking for feedback Open tasks - [ ] Add JWT as Environment Variable - [ ] Provide Symfony Flex Recipe for overall configuration - [ ] Add docs