Godot SDK and Blackholio tutorial

[lisandroct]

Description of Changes

Very small additions to the C# SDK specific for Godot.
I wrote the Godot Blackholio tutorial and updated the Unity one.
I added the image assets necessary for the tutorial.
I added the files for the Godot demo.

API and ABI breaking changes

No breaking changes.

Expected complexity level and risk

1. There's really no risk for current systems or projects, it's all new additions to support nicely(-ish) Godot, new Blackholio demo for Godot and updates to the tutorials.

Testing

• Follow the tutorial and verify everything works.
• Build for Windows and verify it works.
• Build for Linux and verify it works.
• Build SDK
• Publish to Nuget

[rekhoff]

I was only able to get part-way through docs/docs/00100-intro/00300-tutorials/00500-godot-tutorial/00300-part-2.md before hitting a blocker with the implementation.
The tutorial so far it looks good with only some minor nits, but the NuGet package issue will need to get addressed before I can finish reviewing.

[rekhoff]

I have tested the C# Server implementation instructions of the Godot tutorial and left my comments below.
I have also tested the client-godot version in the demo folder and confirmed it works as intended.

[rekhoff]

Requested changes have been made. Marking my approval. Great work on this!

[bfops]

my code-owned file LGTM