Spawner capabilities

[clebergnu]

Is your feature request related to a problem? Please describe.
Different spawners have different capabilities currently implemented. And some spawners may never have some features implemented because of intrinsic limitations. Currently, there's no way for users to know if a capability is available, other than trial and error.

Describe the solution you'd like
Users should be able to tell right away if a feature is available. This can be done through information built into the spawners themselves (preferably), or at the very least through documentation and clear error messages.

This could be done through extended plugin information, implemented at a higher level, but used for spawner plugins:

$ avocado plugins --capabilities
Plugins that spawn tasks and know about their status (spawner):
lxc     LXC (container) based spawner
        Automatic environment provisioning: no
        Avocado deployment: yes
        Environment preservation: yes
        Filesystem sharing: no

podman  Podman (container) based spawner
        Automatic environment provisioning: yes
        Avocado deployment: yes
        Environment preservation: yes
        Filesystem sharing: yes

process Process based spawner
        Automatic environment provisioning: yes
        Avocado deployment: yes
        Environment preservation: no
        Filesystem sharing: yes

Describe alternatives you've considered
A command such as avocado spawners-info could be implemented specifically for extended information of spawners capabilities.