[web] Call baseSetUserAvatar from onImageSelected

Summary:
Once image is successfully uploaded, we make call to `baseSetUserAvatar` from `EditUserAvatarContext`.

As of this diff, users can set emoji, image, ENS avatars (and remove them). What's missing is `ImageAvatarSelectionModal` to handle cropping + some error handling. Those will be handled after the thread avatar work.

---

Depends on D8725

Test Plan:
Works as expected:

{F674875}

Reviewers: ashoat, ginsu

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D8726

web/avatars/edit-user-avatar-menu.react.js

@@ -69,8 +69,11 @@ function EditUserAvatarMenu(): React.Node {
 
   const uploadAvatarMedia = useUploadAvatarMedia();
   const onImageSelected = React.useCallback(
-    event => uploadAvatarMedia(event.target.files[0]),
-    [uploadAvatarMedia],
+    async event => {
+      const uploadResult = await uploadAvatarMedia(event.target.files[0]);
+      baseSetUserAvatar({ type: 'image', uploadID: uploadResult.id });
+    },
+    [baseSetUserAvatar, uploadAvatarMedia],
   );
 
   const imageMenuItem = React.useMemo(