add git-lfs builder

[markudevelop]

why is this not merged? :)

[Reichenbachian]

I agree this should be merged, but for others who find this, I solved with this:

steps:
  - name: "gcr.io/cloud-builders/docker"
    script: |
      apt-get update && apt-get install -y git-lfs
      git lfs install
      git lfs pull
      docker build --no-cache -t ${_IMAGE_NAME} . -f docker/Dockerfile.api