connector should lookup server addr only when unset, not when the value is localhost

[dnephin]

If someone runs the connector with --server-url=localhost the connector will assume that url is wrong and attempt to lookup the server URL from the kubernetes API using the server service name.

infra/internal/connector/connector.go

Lines 95 to 96 in f8689e0

	// server is localhost which should never be the case. try to infer the actual host
	if strings.HasPrefix(u.Host, "localhost") {

I believe this was from a time when we expected the server and connector to often be run in the same cluster.

It seems fine to lookup the server url when the value is empty, but if someone has specified a url for the server, let's not assume it was the wrong value and attempt to override it.

We could choose to remove this lookup entirely, or we could do the lookup only when the value is the empty string.

I think we may want to always default to a server url of api.infrahq.com, which means the server url should never be empty, and we could remove this lookup.