Introduce ext.deadlock - Deadlock Game Coordinator extension

[Aluerie]

🦜 Summary

Deadlock is the newest Valve title. The game seems to have a promising future... so this PR introduces an extension for it. Even though, it's nothing much just bare bones proof of concept that current code structure still works.

I'm not sure what's the end-game for this PR because the game is in alpha state and they change all the protobufs on daily basis, but hey, if anybody wants to mess around with Deadlock Game Coordinator - this PR's branch is a solid foundation.

📝 TODO

• Account Stats
• ???

As I said - not sure what are my plans for this PR. 🙃

✅ Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)