feat(dav): Allow share principals

Signed-off-by: provokateurin <kate@provokateurin.de>

Author: provokateurin

apps/dav/lib/Connector/Sabre/Principal.php

@@ -155,6 +155,11 @@ public function getPrincipalByPath($path) {
 				'uri' => 'principals/system/' . $name,
 				'{DAV:}displayname' => $this->languageFactory->get('dav')->t('Accounts'),
 			];
+		} elseif ($prefix === 'principals/shares') {
+			return [
+				'uri' => 'principals/shares/' . $name,
+				'{DAV:}displayname' => $name,
+			];
 		}
 		return null;
 	}