finish extremely basic implementation of docker credentials

src-tauri/migrations/20240919135710_docker_creds.sql

@@ -7,5 +7,6 @@ CREATE TABLE docker_credentials (
     server_url TEXT UNIQUE NOT NULL,
     username TEXT NOT NULL,
     secret_enc BLOB NOT NULL,
-    nonce BLOB NOT NULL
+    nonce BLOB NOT NULL,
+    FOREIGN KEY(id) REFERENCES credentials(id) ON DELETE CASCADE
 );