Add user interface to example applications

[IanWold]

Summary

Add a shared user interface that all of the example applications can use. The UI should just be a simple chat demo.

What is motivating this feature?

So that newcomers to the project can have working examples that they can easily:

1. See working end-to-end
2. See working in Postgres
3. Interact with

Making it more friendly to get up and going. Not that it's difficult otherwise, but every bit helps.

Detailed Description

1. Add a new shared project in /examples
2. In the shared project, define IChatServer and IChatClient
3. Write a barebones Blazor WASM UI allowing users to "sign in" with a username and join a "chat room" with another user (just typing names in; this should be as noncomplex as possible)
4. Update each example project to serve the chat client at /
5. Update all the READMEs to give specific instructions on running the app, creating multiple servers, and using your own Postgres.

Are there any open questions or investigation needed?

n/a