APP-7497: Add Button client, server, and fake model

[ethanlookpotts]

This adds the button client and server, and registers a button fake model.

Here's a button component properly configured in app:

1. APP-7497: Add Button and Switch APIs api#619
2. APP-7497: Add Button client, server, and fake model #4740
3. APP-7497: Add Switch client, server, and fake models #4741

Change log

I used Cursor quite a bit here:

• Add Button SDK helpers
• Add client and tests
• Add server and tests
• Add inject testutil
• Add fake button implementation and register it
  • This implementation just logs a message when pushed

Review requests

• Code review
• Try a config with the button fake - does it work as expected?