Add --use parameter for one-time execution like flutter create

[timshadel]

I'd really like to be able to do this:

fvm --use 3.0.5 flutter create ....

Version 1 of this would simply run command X with the given version, or fail if the version is not installed.

Version 2: I have no idea if you could easily see that it's creating a new package or app, and then run the code to add the .fvm folder when it's done. That'd be great.

The workaround I have now is to create a new directory for the app, fvm use --force, create the new app using . as the directory name. This works, but it just isn't as intuitive.