title: CircleAvatar() size is not changing inside the appBar
body: <p>So am trying to display circular user image in the home page of an application the image position is at the top left of the screen, after searching and trying i managed to use this approach:</p>
  <pre><code>return Scaffold(
    appBar: PreferredSize(
      preferredSize: Size.fromHeight(100.0),
      child: AppBar(
        backgroundColor: Colors.purple,
        elevation: 0,
        leading: CircleAvatar(
          radius: 10,
          backgroundColor: Colors.black,
          backgroundImage: AssetImage('assets/DefaultImage.png'),
        ),
      ),
    ),
  );
  </code></pre>
  <p>the image is displayed fine but i want to increase the size of it and &quot;radius&quot; is not working at all, i tried to wrap the avatar with container to add some margins but also didn't work.</p>
  <p>my questions are :</p>
  <p>1- how to increase the size of <code>CircleAvatar()</code> inside an <code>AppBar()</code>.</p>
  <p>2- is <code>CircleAvatar()</code> the right choice for user profile image especially if this image was retrieved from firestore?</p>