conmon-rs always opens a namespace, even if it won't be used

[haircommander]

after #1064, conmon-rs always opens a namespace, even if the pod needs a container level namespace. This isn't a behavior problem, but does needlessly add extra mounts and will cause there to be more open files then needed.

[saschagrunert]

@haircommander would it make sense to extend the CLI/Cap'n Proto interface in the same way we have in pinns, for example:

conmonrs pause --ipc       # Unshare to a new IPC namespace
conmonrs pause --ipc=host  # Unshare to the host IPC namespace
conmonrs pause             # Skip unsharing the IPC namespace

[haircommander]

yeah I think so

[haircommander]

also having a target for posterity would be useful (where we just bind mount a path of a namespace)

[haircommander]

I started working on this but didn't finish. I will try to finish next week