There is a version parameter on the app.yml file that can be set to the version you want to run.
Using the official install that is handled using Move from standalone container to separate web and data containers.
True, we try to make it friendly for webmasters from the “drag and drop this zip file contents with FileZilla via FTP”, while ensuring that everyone runs recent, supported and patched versions of all the software in the stack, even their Databases.
For more knowledgeable Discourse admins, pointing to an externally managed database is an environment variable away per Configure Discourse to use a separate PostgreSQL server
Yes, the launcher based flow is not compatible out-of-the-box with container orchestration. That said, it can be made compatible by running ./launcher bootstrap app and pushing the resulting image to a container registry and then running said image via orchestration.
We welcome a pull request to make this possible, as it sounds useful generally. pr-welcome