feat: add build envars to Dockerfiles and images

[DerekRoberts]

This is the exciting part.

env:
  dockerfile: ${{ steps.vars.outputs.build_file }}
shell: bash
run: |
  # Add build envars to Dockerfile
  echo "ENV BUILDER_IMAGE=ghcr.io/${{ github.repository }}/${{ inputs.package }}:${{ inputs.tag }}" >> ${{ env.dockerfile }}
  echo "ENV BUILDER_PACKAGE=${{ inputs.package }}" >> ${{ env.dockerfile }}
  echo "ENV BUILDER_REPO=${{ github.repository }}" >> ${{ env.dockerfile }}
  echo "ENV BUILDER_TAG=${{ inputs.tag }}" >> ${{ env.dockerfile }}

[mishraomp]

LGTM , noyce