Support OpenRC

[B83C]

The title is self evident. Would be great to have support on OSes like alpine.

[psviderski]

I appreciate the interest in supporting lightweight distros like Alpine but this will likely stay out of scope for the near future.

Note that it should technically be supported even now but you'd need to install provision the machine manually (install uncloud binaries, configure openrc services to run uncloudd and uncloud-corrosion daemons, create uncloud user/group, etc.). Essentially, replicate the configuration in the install.sh that is run as part of uc machine init/add.

Then you should be able to initialise the provisioned machine as a new cluster or as part of an existing cluster with uc machine init/add --no-install.