feat: add gameReady

[hubertusputu1]

Add gameReady on gameLobby

Description

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ ] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.

[hubertusputu1]

https://linear.app/patondev/issue/PAT-82/if-lobby-custom-do-not-show-game-ready-page

[npaton]

Discussed with @hubertusputu1, this would actually not be needed, we can just use get/set on game (gameLobby) to communicate between the beforegameinit callback and the custom lobby component.