init intro toolchain

[kpenfound]

Staring with 3 checks:

• "install a toolchain": this is passing because they have intro installed! I thought it would be important to at least see what a passing check looks like from the beginning
• "login to dagger cloud": makes sure they are logged in. If they dont have an org created yet, dagger login will kick-off that flow
• "install more toolchains": using a hardcoded list of toolchains we've built so far, checks for project indicators that they should use each one and recommends the proper dagger toolchain install for it. For example, if you run dagger check in this repo, it will recommend the go toolchain by outputting Install go: dagger toolchain install github.com/dagger/dagger/toolchains/go

Its in Go instead of Dang because it might be the first toolchain people look at, and I don't want to scare them away with a language they haven't heard of before.

@TomChv if you have any more toolchains to add like vitest, hopefully this format is easy to maintain!