Add basic SwiftUI Avatar picker

[pinarol]

Closes #

Description

Adds a very basic AvatarPickerView. It takes in email and token then,

• Fetches the avatars and displays them in a grid layout that can adjust itself according to the device width
• Shows the selected avatar with a border.
• Shows a loading indicator.
• Allows retrying the fetch if an error occurs.
• If the result is empty, shows an appropriate message.

(We don't have a design yet but when we do, we'll just need to update the UI hopefully. For now all I care about is to handle those states.)

• Also, it uses system fonts and colors so it adapts font size changes and light/dark modes.

These features don't exists yet:

• Picking a different avatar and displaying a success toast
• Uploading a new avatar

Testing Steps

Demo app > Avatar Picker View

You can also play with the #Preview items under AvatarPickerView.swift

You will need to capture an accessToken, I captured mine via changes in this branch etoledom/avatar-picker