reverseproxy: Avoid returning an error if host address is not an IP address

[JordiSubira]

I am using the reverseproxy module with a custom underlay network, more concretely a SCION network. The SCION underlay network doesn't use IP addresses as host addresses. More concretely, the retrieved addrPort value on https://github.com/caddyserver/caddy/blob/v2.9.0-beta.3/modules/caddyhttp/reverseproxy/reverseproxy.go#L687 will yield and address of the following format [isd-as,ipv4]:port or [isd-as,ipv6%zone]:port.

An error is returned on https://github.com/caddyserver/caddy/blob/v2.9.0-beta.3/modules/caddyhttp/reverseproxy/reverseproxy.go#L740 after netip.ParseAddr(clientIP), in turn, returns an error. I would suggest to ignore the trusted proxy check if netip.ParseAddr(clientIP) returns an error, for example something similar to this:

...
trusted := caddyhttp.GetVar(req.Context(), caddyhttp.TrustedProxyVarKey).(bool)
clientIP, _, _ = strings.Cut(clientIP, "%")
ipAddr, err := netip.ParseAddr(clientIP)
if err == nil {
	// Check if the client is a trusted proxy
	for _, ipRange := range h.trustedProxies {
		if ipRange.Contains(ipAddr) {
			trusted = true
			break
		}
	}
}
...

Note that SplitHostPort here is able to split non-ip hosts, so it seems more appropriate to consider that the host address is not necessarily an IP address .This change would maintain the current behavior (meaning that it would not break something that is already working) while allowing for other host address types.