Move the package directory to a separate repo

[Looooong]

In essence, this repo is a development project that includes the Mixture package. I would love to have the package directory moved to a separated repo and included in this repo as a git submodule.

The reason behind this is that I cannot use registry package because I want to make a few modifications. On the other hand, I also cannot use local package because I cannot share the modification with my colleague. In my use case, I want to fork ONLY the package as a repo and can easily add this forked repo to Unity Package Manager using git URL. By doing so, I can collab with my colleague on both the Unity project along with the forked repo.

Basically, you can setup your repos like one of the following:

• Use Mixture repo for dev project and use Mixture-package repo for package.
• Use Mixture repo for package and use Mixture-dev for dev project.
• Use Mixture repo for package and move the dev project info a orphaned branch under Mixture repo. This is what I have done for my Unity package where the dev project is moved to branch legacy and is also distributed in Releases as demo project

The later 2 options are preferable as people can contribute directly to the already popular repo.