build: fix stdin handling when building with controller

[crazy-max]

fixes #2368

When building in experimental mode we are using the controller which handles io forwarding operations, such as copying data from a reader to a writer and therefore locks stdin from being read in

buildx/build/opt.go

Line 384 in 5c29e6e

magic, err := buf.Peek(archiveHeaderSize * 2)

To fix this we can skip forwarding if invoke is not used as it seems to be handled only for this case. We also have a clear condition making it not possible to use a Dockerfile or context from stdin if invoke is used:

buildx/commands/build.go

Lines 397 to 400 in 0a3e5e5

	if options.invokeConfig != nil && (options.dockerfileName == "-" || options.contextPath == "-") {
	// stdin must be usable for monitor
	return nil, errors.Errorf("Dockerfile or context from stdin is not supported with invoke")
	}

This should mitigate this issue but might need a deeper look as follow-up

[ktock]

Thanks! LGTM