New Group administration: update title and avatar

ts/util/canvasToArrayBuffer.ts

@@ -0,0 +1,17 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+export async function canvasToArrayBuffer(
+  canvas: HTMLCanvasElement
+): Promise<ArrayBuffer> {
+  const blob: Blob = await new Promise<Blob>((resolve, reject) => {
+    canvas.toBlob(result => {
+      if (result) {
+        resolve(result);
+      } else {
+        reject(new Error("Couldn't convert the canvas to a Blob"));
+      }
+    }, 'image/webp');
+  });
+  return blob.arrayBuffer();
+}