Draft: Enable Docker service when installing Guacamole

Fixes #455 (closed).

How to Test

Go to https://try-dev.exosphere.app or https://exosphere.jetstream-cloud.org. Launch a new instance from one of the Jetstream featured API images. Wait for Guacamole (Web Terminal) to become available. Shelve the instance and then unshelve it again. Confirm that the Docker service is started, and (after a browser tab refresh) Guacamole becomes available on its own.

Screenshots

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