Import configuration with libsmbconf API

[phlogistonjohn]

Currently, when sambacc imports samba configuration from it's own JSON based fomat it uses the net conf import command line. Future versions of Samba will have a python binding for the smbconf library. This library can be used to read a text based config (smb.conf) or read/write registry based configuration. This would allow us to use the library directly rather than generating a text based configuration and shelling out to net command to update the registry.

It may also make post-init configuration updates simpler and easier to see exactly what is changing.

[phlogistonjohn]

This is partially implemented as PR #85 brought in smbconf support to help parse smb.conf text files in the AD DC case. I started looking into this but found that the registry.tdb reference in samba is a singleton that is only loaded once per process. This makes adding unit tests to match netcmd_loader a bit more challenging. However, that only impacts the unit tests so this is looking doable soon.