cmd/go: add a better error message when in a module outside workspace
When the user is trying to list or build a package in a module that's
outside of the workspace provide a more clear message hinting to the
user that they can add the module to the workspace using go work use.
Fixes #51604
Change-Id: I1202ecb2f22fd6351bfdec88ed613b8167687fb7
Reviewed-on: https://go-review.googlesource.com/c/go/+/400014
Run-TryBot: Michael Matloob <matloob@golang.org> Reviewed-by: Michael Matloob <matloob@golang.org>
Auto-Submit: Michael Matloob <matloob@golang.org> Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>