dns: Add `AppleDnsResolverConfig.include_unroutable_families` config (#20527)

If set, the resolver will avoid the system's heuristics to only return
IPv4 or IPv6 addresses that it considers to be "routable", instead
returning all possible IPv4 or IPv6 addresses. This setting is
ignored if the DNS lookup family is set to v4-only or v6-only.

This may be a useful setting to specify if the addresses considered
unroutable by the system's heuristics may in practice be routable.

Signed-off-by: JP Simard <jp@jpsim.com>

Mirrored from https://github.com/envoyproxy/envoy @ 60a13f30a4e425c907607fab96efee0ed2afcf22

envoy/extensions/network/dns_resolver/apple/v3/apple_dns_resolver.proto

@@ -15,4 +15,12 @@ option (udpa.annotations.file_status).package_version_status = ACTIVE;
 
 // Configuration for apple DNS resolver.
 message AppleDnsResolverConfig {
+  // The resolver will avoid the system's heuristics to only return
+  // IPv4 or IPv6 addresses that it considers to be "routable", instead
+  // returning all possible IPv4 or IPv6 addresses. This setting is
+  // ignored if the DNS lookup family is set to v4-only or v6-only.
+  // This should remain false in the vast majority of cases, but may be
+  // useful when performing custom filtering of addresses, such as with
+  // Happy Eyeballs.
+  bool include_unroutable_families = 1;
 }