Make working directory of build command configurable

[dmikusa]

Describe the Enhancement

Presently, the working directory is always /workspace (i.e. the app root). We should make this configurable.

https://github.com/paketo-buildpacks/libbs/blob/main/application.go#L56-L64

We will need to enable configuration options to pass this through. It maybe a little tricky to do this without breaking the present API, so we may need to hold this for v2.

Motivation

This allows the library to be more flexible for build tools and allows them to run the build command from a different location.