Build github actions workflow

[agouin]

Build github actions workflow so that heighliner images can be built and push from an importable workflow.

Examples

With built-in chain config

      - name: Build and push heighliner Docker image
        uses: heighliner/build-push-action@v1
        with:
          chain: gaia

Custom chain config

      - name: Build and push heighliner Docker image
        uses: heighliner/build-push-action@v1
        with:
          chain: somechain
          dockerfile: cosmos
          build-target: install
          build-env:
            - LEDGER_ENABLED=false
            - BUILD_TAGS=muslc
          binaries:
            - /go/bin/somechaind

[bigs]

I'm working on this, and will have a version up soon. It's going to be homed in my Git org, but I can transfer it if it passes muster.

[bigs]

The MVP is up at burnt-labs/heighliner-action