Create a vm for footer

src/viewmodels/FooterViewModel.ts

+import { ViewModel } from "hydrogen-view-sdk";
+import { IChatterboxConfig } from "../types/IChatterboxConfig";
+
+export class FooterViewModel extends ViewModel {
+    private _config: IChatterboxConfig;
+
+    constructor(options) {
+        super(options);
+        this._config = options.config;
+    }
+
+    openChatterboxLink() {
+        const link = this._config.footer?.chatterbox_link;
+        if (link) {
+            (window as any).sendOpenLink(link);
+        }
+    }
+
+    openMatrixLink() {
+        const link = this._config.footer?.matrix_link;
+        if (link) {
+            (window as any).sendOpenLink(link);
+        }
+    }
+}