Add support for excluding targets in `buck2 build`

At work, we generate test targets with different sets of modifiers so that `buck2 test ...` builds/test a project with various configurations.
We tag the targets with non-default modifiers with an `extra_test` label, so that we can do `buck2 test --exclude extra_test ...` for faster iteration cycles.

As far as I can tell, there is no way to do the same thing for `buck2 build`. Is this intentional?