Implement the `onPressSetAvatar` function. This diff handles the user experience for when a user presses the save avatar button.
Here's an outline of the experience from a high level:
# We attempt to call the update user avatar endpoint
# While we are making this attempt, both the save and reset button will be disabled and a spinner will render on top of the emoji avatar
# If we are successful we will show a toast message saying the avatar has been updated
# If we fail then an alert will display telling the user something went wrong and to try again later
Depends on D7323