Add Docker hub release workflow

[bobbyiliev]

Adding a release workflow to publish the Docker image for the datagen to Docker Hub.

Before we merge this, we need to add a DOCKER_USERNAME and DOCKER_PASSWORD secret.

Closes #37

[chuck-alt-delete]

Here are a couple of suggested changes:

name: Publish Docker image

on:
  push:
    branches: ["main"]
    tags: ["v*"]

jobs:
  push_to_registry:
    name: Push Docker image to Docker Hub
    runs-on: ubuntu-latest
    steps:
      - name: Check out the repo
        uses: actions/checkout@v3

      - name: Use buildx for multi-platform images
        uses: docker/setup-buildx-action@v2

      - name: Log in to Docker Hub
        uses: docker/login-action@v2
        with:
          username: ${{ secrets.DOCKER_USERNAME }}
          password: ${{ secrets.DOCKER_PASSWORD }}
      
      - name: Extract metadata (tags, labels) for Docker
        id: meta
        uses: docker/metadata-action@v4
        with:
          images: materialize/datagen
          tags: |
            type=semver,pattern={{major}}.{{minor}}
      
      - name: Build and push Docker image
        uses: docker/build-push-action@v4
        with:
          context: .
          push: true
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}

Instead of using SHA values for the action version, I just stuck with latest major version. I think that will suffice. If we want SHA values, we should look up what the latest for each is, because I think some of the ones in this PR are quite out of date.

I added a step for buildx, because it apparently handles multi platform builds for us (i.e. ARM and x86).

For the meta step, I added semantic versioning. It will automatically create a docker tag based on the semantic version as well as a latest tag. See example. So for a tag v0.1.0 it would create docker tag 0.1.0 and latest.

What do you think?

[bobbyiliev]

Good points! Just updated this with the suggested changes!

[benesch]

I added Docker credentials to this repository. The username is materializebot and the password is in DOCKER_HUB_MATERIALIZEBOT_API_KEY. Here's an example from another repository: https://github.com/MaterializeInc/rr/blob/0afcd9677bbf8a3a851318b592fbb23c3aece57a/.github/workflows/ci.yml#L23-L24

[bobbyiliev]

Thank you @benesch! I just updated the credentials accordingly!