fix(signed-request): trigger metadata insert with default value manually

Signed-off-by: Maxence Lange <[email protected]>

lib/private/Security/Signature/SignatureManager.php

@@ -353,6 +353,7 @@ private function insertSignatory(Signatory $signatory): void {
 		$time = time();
 		$signatory->setCreation($time);
 		$signatory->setLastUpdated($time);
+		$signatory->setMetadata($signatory->getMetadata()); // trigger insert on field metadata using current or default value
 		$this->mapper->insert($signatory);
 	}