Support configuring trino-lb endpoint instead of address

[sbernauer]

Came up in #100 (comment)

Basically, change

trinoLb:
  externalAddress: https://127.0.0.1:8443

to

trinoLb:
  externalEndpoint: https://127.0.0.1:8443/my/subpath

However, this is a breaking change and needs some rework of trino-lb.
Think of e.g.

fn change_next_uri_to_trino_lb(next_uri: &Url, trino_lb_addr: Url) -> Url {
    let mut result = trino_lb_addr;
    result.set_path(next_uri.path());
    result
}

This obviously needs to be changed to handle subpaths in the trino-lb endpoint