support multiple proxy clients with skywire-cli proxy

[0pcom]

its possible currently to configure multiple proxy clients for the visor - by manually changing the visor's config as shown

We should make this configurable during runtime with some changes to skywire-cli proxy

skywire-cli proxy status needs to show a detailed status for any running instances of the proxy client.

skywire-cli proxy start should have a flag that allows an additional proxy to be started on the next available port if an instance is already started.

skywire-cli proxy stop should have a flag to stop all the proxy clients.