res_ari: Add http prefix to generated docs

updated the uri handler to include the url prefix of the http server
this enables res_ari to add it to the uris when generating docs

Change-Id: I279335a2625261a8492206c37219698f42591c2e
(cherry picked from commit 6f448f32fe)

include/asterisk/http.h

@@ -101,6 +101,7 @@ struct ast_http_uri {
 	AST_LIST_ENTRY(ast_http_uri) entry;
 	const char *description;
 	const char *uri;
+	const char *prefix;
 	ast_http_callback callback;
 	unsigned int has_subtree:1;
 	/*! Structure is malloc'd */