cli/cmd/go-encore-wrapper: new command

[eandre]

This adds a new command, go-encore-wrapper, that is designed to wrap the "go" command and forward certain commands to the "encore" CLI, like running tests.

The purpose is to build a better integration with tools like vscode-go that only support replacing the "go" tool with another tool that has the same command structure.

With this change, users will be able to configure vscode-go to use Encore when appropriate simply by defining:

"go.alternateTools": {"go": "go-encore-wrapper"}

[encore-cla[bot]]

All committers have signed the CLA.

[eandre]

Let's hold off on merging this until we know more about where we're going with https://github.com/golang/vscode-go/issues/2238.