epic: separate explorer repositories

[menduz]

With the objective of generating independent release cycles and to foster easier modifications of Decentraland, some components should be separated into their own repositories. I believe this would lower the entry barrier for new contributors and also make the code structure less scary and easier to understand.

Also, having separated repositories means some hard interfaces should be set in place, those interfaces will help establish long-term backwards compatible protocols and components.

Technical definitions of interfaces

• [x] Website<>Kernel protocol https://github.com/decentraland/kernel-interface/
• [ ] Kernel<>Renderer protocol https://github.com/decentraland/renderer-protocol https://github.com/decentraland/explorer-technical-backlog/issues/2
• [ ] Runtime<>User generated code protocol https://github.com/decentraland/posix (pending impl)

Tasks

• [x] Inversion of control of unity-renderer loading cycle https://github.com/decentraland/unity-renderer/pull/689
• [x] create PR in kernel https://github.com/decentraland/explorer-technical-backlog/issues/19 https://github.com/decentraland/explorer-website
• [x] Publish @dcl/kernel in https://github.com/decentraland/kernel
• [x] Separate unity-renderer in its own repository https://github.com/decentraland/unity-renderer/
• [x] Separate build-ecs in its own repository https://github.com/decentraland/js-sdk-toolchain/tree/main/packages/%40dcl/build-ecs
• [x] Separate dcl-amd in its own repository https://github.com/decentraland/js-sdk-toolchain/tree/main/packages/%40dcl/amd
• [x] #21
• [x] Separate decentraland-ecs in its own repository, skip publishing https://github.com/decentraland/sdk/issues/1 https://github.com/decentraland/sdk/issues/4
• [x] decentraland-ecs now uses references to @dcl/kernel and @dcl/unity-renderer, not embeding artifacts
• [x] CLI gets adaptation code to use the new file structure https://github.com/decentraland/sdk/issues/12