Switch to GrapheneOS based on Android 12.1

[ypid]

Closes: #45, #47, #41

Build GrapheneOS with our patches successfully for sargo.

Note, this now includes aosp-build as submodule to avoid redundancy and to support make review. Note also that this drops the local Docker image. I think it is not needed. Lets keep it simple and have all the dependencies in aosp-build.

[ypid]

@lrvick Can you make branch '11' the default one in both this repo and https://github.com/hashbang/aosp-build? This would than match the way GrapheneOS does it. Also, can you remove the protection on the master branch? It prevents me from pushing signed merge commits. The master branch can then also be deleted. It is outed. But I can also do that I guess in case you remove the protection.