automatically open code-workspace on dev container

The user's current work is:

1. Spin up a Docker in a remote machine (workspace folder is mounted to this Docker).
2. SSH into this machine using the Remote-SSH extension.
3. Attach into the running Docker with the Dev Container extension.
4. Now we are in the workspace, BUT we need to select File > Open Workspace from File to actually start working in the Docker workspace.

Currently, the most frustrating step is the last one, which I think is the easiest to solve - somehow tell the Dev Container where the code-workspace file is so it will automatically attach to the workspace. By that, we eliminate step 4.

Another improvement that is probably harder is to see directly in the Remote-SSH view the Dockers we can attach to (and by that combine steps 2+3).

Thanks for all the work on those extensions! They are great!