Allow start scripts to provide multiple server IPs

Currently start scripts specify the server IP and port, but what if it could provide multiple e.g.

- an IPv6 address
- an IPv4 address
- a TURN relay server

the engine could then try them one by one in order, this way a client behind ISP level NAT that requires special techniques to reach via IPv4 may get a more direct connection via IPv6, before falling back to a pre-negotiated relay server

No files or tests are named. Start by tracing how start scripts pass the server IP and port into the engine and how clients establish connections; define how an ordered list containing IPv6, IPv4, and TURN endpoints should be represented and attempted. Done means clients try the supplied endpoints in order and fall back when an earlier connection fails.

Written by the indexing model from the issue text.