Update Avatar and Username example in iframe playground

[matthova]

This PR updates our usage of discriminator % 5 for default avatar URIs to instead follow the new default avatar uri pattern called out in the docs https://discord.com/developers/docs/reference#image-formatting-cdn-endpoints
More specifically

• Updates auth in iframe playground to store guild member info as a part of the auth object
• Updates iframe playground to render the username and avatar per new pattern
• Updates react-colyseus to render the username and avatar per new pattern

Iframe playground with default avatar and global_name

Iframe playground with guild-specific avatar and name

React colyseus with all the things