feat(studio): optional pinned-key field in the store-add form

The module-store manager's 'Add a store' form gains an optional PEM
public-key field; when set it pins that publisher key to the store
(per-store signing trust). Localized DE/EN.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/data/hub.dart

@@ -220,8 +220,14 @@ class HubService {
     required String name,
     required String url,
     String bearerEnv = '',
+    String pinnedPubkeyPem = '',
   }) =>
-      _client.addStore(name: name, url: url, bearerEnv: bearerEnv);
+      _client.addStore(
+        name: name,
+        url: url,
+        bearerEnv: bearerEnv,
+        pinnedPubkeyPem: pinnedPubkeyPem,
+      );
 
   /// Drop a configured store by name (the bundled seed cannot be removed).
   Future<RemoveStoreResponse> removeStore(String name) =>