Allow customizing build dir

[MOZGIII]

Docker allows specifying the build directory: docker build target/artifacts. People usually use it with docker build ., but it is useful at times.

We're relying on using non-. build dir in our build system, so draft doesn't work for us as it doesn't allow customizing build dir (only Dockerfile location).

It would be great if the support for customizing build dir was added to draft.

[squillace]

that would be a great thing to add, you're right. Unfortunately, we do not have resources to apply to draft at the moment; if things change, this is on the list.