Support for gRPC-Web

[ghost]

If I attempt to add github.com/grpc/grpc-web to my plugins directive, powerproto attempts to go install it, which (of course) fails.

panic: failed to execute /usr/bin/go install github.com/grpc/grpc-web@master in , stderr: go: downloading github.com/grpc/grpc-web v0.0.0-20211119232535-3fcc2a2a8a04
go install github.com/grpc/grpc-web@master: module github.com/grpc/grpc-web@master found (v0.0.0-20211119232535-3fcc2a2a8a04), but does not contain package github.com/grpc/grpc-web
, exit code 1, exit status 1

goroutine 1 [running]:
github.com/storyicon/powerproto/pkg/bootstraps.StepInstallPlugins(0xb5a5c0, 0xc00011db00, 0xb603a8, 0xc00022e300, 0xc000274020, 0x1, 0x1, 0x0, 0x0)
        github.com/storyicon/[email protected]/pkg/bootstraps/build.go:215 +0xc88

When I install protoc-gen-grpc-web, powerproto won't detect it, because it's not passed to the plugin list (due to above.)

I also didn't see it in the output option list shown during init.