Add some defaults for subuid/subgid ranges
As the containers are isolated by default, they currently fail to configure on a standard NixOS system, because the default subuid/subgid range is too small.
Solutions:
- make containers non-isolated by default, and add a note to the
isolated
option to inform the user that they need to configure bigger ranges for isolated containers - make this module automatically configure bigger ranges
Note: LXD seems to require at least 65536 UIDs in addition to the UIDs required for isolated containers. Their documentation recommends setting up a 1000000000 (billion) sized UID range.