[FEATURE] Support `--jobs N` flag on buildah bud about buildah-build

[akostadinov]

+1, for some reason adding as extra args seems to be ignored

      - name: Build image
        id: build-image
        uses: redhat-actions/buildah-build@v2
        with:
          tags: ${{ steps.meta.outputs.tags }}
          platforms: linux/amd64,linux/s390x,linux/ppc64le
          labels: ${{ steps.meta.outputs.labels }}
          layers: false
          oci: true
          tls-verify: true
          extra-args: |
            --squash
            --jobs=3
          build-args: |
            PORTA_IMAGE=quay.io/3scale/porta:free-sphinx
          containerfiles: |
            Containerfile