Add missing OPTIONAL_API and ARI dependences.

I've audited all modules that include any header which includes
asterisk/optional_api.h.  All modules which use OPTIONAL_API now declare
those dependencies in AST_MODULE_INFO using requires or optional_modules
as appropriate.

In addition ARI dependency declarations have been reworked.  Instead of
declaring additional required modules in res/ari/resource_*.c we now add
them to an optional array "requiresModules" in api-docs for each module.
This allows the AST_MODULE_INFO dependencies to include those missing
modules.

Change-Id: Ia0c70571f5566784f63605e78e1ceccb4f79c606

res/res_pjsip_outbound_registration.c

@@ -2290,4 +2290,5 @@ AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_LOAD_ORDER, "PJSIP Outbound Regist
 	.unload = unload_module,
 	.load_pri = AST_MODPRI_APP_DEPEND,
 	.requires = "res_pjsip",
+	.optional_modules = "res_statsd",
 );