feat: implement connection and database types

types/database.ts

@@ -0,0 +1,14 @@
+import { Id } from "./common";
+
+export interface Database {
+  connectionId: Id;
+  name: string;
+  tableList: Table[];
+}
+
+interface Table {
+  name: string;
+  // structure is a string of the table structure.
+  // It's mainly used for providing a chat context for the assistant.
+  structure: string;
+}