Hello, it would be cool to split the setup-nim-action@v1 into a choosenim action

[ringabout]

Sometimes users need to test different Nim versions with choosenim, e.g. running a bisect in https://github.com/juancarlospaco/nimrun-action

[jiro4989]

I have wanted to remove the dependency on choosenim from setup-nim-action for some time.
And I removed the dependency on setup-nim-action@v2.

Anyone can create Custom Actions, so if you want choosenim, you can create them yourself.