Multi Deployment - multiple dmsg-discovery configuration [WIP]

[0pcom]

This PR attempts to support configuration of multiple dmsg discovery servers or multiple dmsg networks.

For dmsg curl or any short-lived dmsg client this can be implemented as fallback such that if the client configured with the first specified dmsg discovery makes a request which returns an error (i.e. dmsg errors - not http status code errors) or no response, the request is attempted again with a dmsg client configured with the next specified dmsg discovery server.

For long-lived dmsg clients, or those which wrap an HTTP or TCP server application OR the dmsg client of the skywire visor, it will be required to use as many clients simultaneously as the number of dmsg-discovery servers which are specified, and to connect to or register the client in all configured dmsg discoveries simultaneously.

For the dmsg server it will be required to connect to both dmsg discoveries ; and separate or different ports must be used for each configured dmsg-discovery.

NOTE: the retry logic for dmsg clients is very weak, currently. If the request cannot be fulfilled from a dmsg server that the client is currently connected to, but the client it is attempting to connect to is itself connected to more than one dmsg server, the first client should attempt to connect to the second one via the other dmsg server before using a client which is connected to another dmsg discovery server.

PR is WIP