Addresses #15663.

This PR saves the entire coder home directory in a Docker volume to make the dev tunnel URL persistent across container restarts.

I initially wanted to persist only the config directory, but Docker Compose cannot set permissions on a named volume unless the directory it’s mounted on already exists within the container. The /home/coder/.config directory, however, is not created by default in the Dockerfile. When I attempt to mount it, Docker creates it with root permissions, and Coder cannot write to it. I encounter the following error:

coder-1     | Started HTTP listener at http://0.0.0.0:7080
coder-1     | Opening tunnel so workspaces can connect to your deployment. For production scenarios, specify an external access URL
coder-1     | Encountered an error running "coder server", see "coder server --help" for more information
coder-1     | error: create tunnel: read or generate config: get config path: mkdirall config dir "/home/coder/.config/coderv2": mkdir /home/coder/.config/coderv2: permission denied

Creating the directory in the Dockerfile would resolve the issue for new images but would break docker-compose.yml for all existing Coder images. Mounting the entire home directory avoids this problem, but it makes it less clear to admins which files need to be persisted. It’s a trade-off - I believe keeping Docker Compose backwards-compatible is more important, and I hope the added comment clarifies the purpose of the volume for new users.