feat: add build cache location support for buildah

Allow configuration of the build cache location for buildah the same as for kaniko.

/!\ Replaces $KANIKO_SNAPSHOT_IMAGE_CACHE with $DOCKER_BUILD_CACHE_LOCATION
A partial backward compatibility is ensured for projects using the $KANIKO_SNAPSHOT_IMAGE_CACHE variable but not with the 'kaniko-snapshot-image-cache' input that would fail the pipeline.

Signed-off-by: Weimann, Simon <simon.weimann@ruv.de>