resolved: introduce the _localdnsstub and _localdnsproxy special hostnames for 127.0.0.54 + 127.0.0.53

Let's give these special IP addresses names. After all name resolution
is our job here.

Fixes: #23623

src/basic/hostname-util.h

@@ -60,4 +60,12 @@ static inline bool is_outbound_hostname(const char *hostname) {
         return STRCASE_IN_SET(hostname, "_outbound", "_outbound.");
 }
 
+static inline bool is_dns_stub_hostname(const char *hostname) {
+        return STRCASE_IN_SET(hostname, "_localdnsstub", "_localdnsstub.");
+}
+
+static inline bool is_dns_proxy_stub_hostname(const char *hostname) {
+        return STRCASE_IN_SET(hostname, "_localdnsproxy", "_localdnsproxy.");
+}
+
 int get_pretty_hostname(char **ret);