Ampache API: Make advanced_search args operator and type optional

The `operator` now defaults to 'and' and `type` to 'song'. The API
specification defines these arguments as required but the changed
behavior matches the actual implementation of the genuine Ampache
server. At least the Foam client relies on this behavior.

CHANGELOG.md

@@ -3,6 +3,7 @@
 ### Added
 
 ### Changed
+- Ampache API: Make `advanced_search` arguments `operator` and `type` optional
 
 ### Fixed
 

lib/Controller/AmpacheController.php

@@ -1170,7 +1170,7 @@ protected function bookmark_delete(int $filter, string $type) : array {
 	/**
 	 * @AmpacheAPI
 	 */
-	protected function advanced_search(string $type, string $operator, int $limit, int $offset=0, bool $random=false) : array {
+	protected function advanced_search(int $limit, int $offset=0, string $type='song', string $operator='and', bool $random=false) : array {
 		// get all the rule parameters as passed on the HTTP call
 		$rules = self::advSearchGetRuleParams($this->request->getParams());