feat: add incus/LXC connector

[romain-dartigues]

Dear pyinfra,

I started adding a LinuxContainers / Incus connector.
It is much a work in progress and I would appreciate feedback.

Actually it can:

• work with local or remote incus/lxc server
• execute action on all instances of the targeted incus/lxc server

It relies on the agent to be running on the targeted instance, when not the case it won't be able to do much more than getting it's name from the list and it's IPv4 address if there is one.

Examples:

# on remote servers:
pyinfra @incus/incus.example.net:instance_name files.get src=/tmp/n.log dest=n.log

pyinfra --debug -vvv --dry @incus/incus.example.net: fact server.LinuxName

# same, but target the local server
pyinfra @incus/instance_name files.get src=/tmp/n.log dest=n.log
pyinfra --debug -vvv --dry @incus/ fact server.LinuxName

[romain-dartigues]

Obviously I did my code without looking around...
Refs: #677, #1282