cache user's metdata in db

src-tauri/migrations/20230418013219_initial_data.sql

@@ -47,4 +47,13 @@ CREATE TABLE
     key TEXT NOT NULL,
     value TEXT NOT NULL,
     created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
+  );
+
+-- create metadata table
+CREATE TABLE
+  metadata (
+    id TEXT NOT NULL PRIMARY KEY,
+    pubkey TEXT NOT NULL,
+    content TEXT NOT NULL,
+    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
   );