res_prometheus: Optional load res_pjsip_outbound_registration.so

Switched res_pjsip_outbound_registration.so dep to optional. Added
module loaded check before using it.

ASTERISK-30101 #close

Change-Id: Ia34f1684d984e821fbdd4de8911f930337703666

res/res_prometheus.c

@@ -974,8 +974,13 @@ static int load_module(void)
 	if (cli_init()
 		|| channel_metrics_init()
 		|| endpoint_metrics_init()
-		|| bridge_metrics_init()
-		|| pjsip_outbound_registration_metrics_init()) {
+		|| bridge_metrics_init()) {
+		goto cleanup;
+	}
+	
+	if(ast_module_check("res_pjsip_outbound_registration.so")) {
+		/* Call a local function, used in the core prometheus code only */
+		if (pjsip_outbound_registration_metrics_init())
 		goto cleanup;
 	}
 
@@ -1004,6 +1009,7 @@ AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_GLOBAL_SYMBOLS | AST_MODFLAG_LOAD_
 	.load_pri = AST_MODPRI_DEFAULT,
 #ifdef HAVE_PJPROJECT
 	/* This module explicitly calls into res_pjsip if Asterisk is built with PJSIP support, so they are required. */
-	.requires = "res_pjsip,res_pjsip_outbound_registration",
+	.requires = "res_pjsip",
+	.optional_modules = "res_pjsip_outbound_registration",
 #endif
 );