First cut to moodle-php-apache multiarch builder

First attempt to switch the automated building of moodle-php-apache
images from DockerHub to GHA. Main reason being that the former doesn't
support multiarch builds (only multiarch storage).

Link: docker/hub-feedback#1874

Experimentally we'll be, also, sending the images to both DockerHub
and GitHub registries in case we need to switch some day.

This requires:

1. Some secrets to be created:
  - DOCKERHUB_USERNAME
  - DOCKERHUB_TOKEN (write perms)
  - DOCKERHUB_PASSWORD, grrr, descriptions cannot be updated using PATs,
    see peter-evans/dockerhub-description#10
  - GH_USERNAME
2. Autobuilds @ DockerHub to be disabled (this takes exactly on them)

Author: stronk7

.github/workflows/buildx_and_publish.yml

@@ -0,0 +1,77 @@
+name: Docker multiarch publish
+
+on: push
+
+env:
+  REPOSITORY: moodle-php-apache
+  DOCKERHUB_OWNER: moodlehq
+  GH_OWNER: moodlehq
+
+jobs:
+  Build:
+    # Completely avoid forks to try this workflow.
+    if: github.repository_owner == 'moodlehq'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      # Calculate the tags to be pussed to the registries.
+      - name: Calculate image tag names
+        id: calculatetags
+        uses: docker/metadata-action@v3
+        with:
+          images: |
+            ${{ env.DOCKERHUB_OWNER }}/${{ env.REPOSITORY }}
+            ghcr.io/${{ env.GH_OWNER }}/${{ env.REPOSITORY }}
+          flavor: |
+            latest=false
+          tags: |
+            type=raw,value=dev
+
+      # https://github.com/docker/setup-qemu-action#usage
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+
+      # https://github.com/marketplace/actions/docker-setup-buildx
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+
+      # https://github.com/docker/login-action#docker-hub
+      - name: Login to Docker Hub
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      # https://github.com/docker/login-action#github-container-registry
+      - name: Login to GitHub Container Registry
+        uses: docker/login-action@v1
+        with:
+          registry: ghcr.io
+          username: ${{ secrets.GH_USERNAME }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      # https://github.com/docker/build-push-action#multi-platform-image
+      - name: Build and push to Docker Hub and Github registries
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          file: Dockerfile
+          platforms: linux/amd64,linux/arm64
+          push: true
+          tags: ${{ steps.calculatetags.outputs.tags }}
+
+      # https://github.com/peter-evans/dockerhub-description
+      # It's horrible that we need to use password here instead of PAT, because
+      # that's only available via CLI what defeats 2FA. Anyway, we need to
+      # auto-update de description, so using it (till available via PAT).
+      # Link: https://github.com/peter-evans/dockerhub-description/issues/10
+      # Note that we only update the description with the master branch version.
+      - name: Set Docker Hub description from README.md
+        if: github.ref == 'refs/heads/master'
+        uses: peter-evans/dockerhub-description@v2
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_PASSWORD }}
+          repository: ${{ env.DOCKERHUB_OWNER }}/${{ env.REPOSITORY }}

README.md

@@ -20,29 +20,31 @@ A Moodle PHP environment configured for Moodle development based on [Official PH
 | PHP 7.0      | Jessie  | 7.0-jessie       | [![Build Status](https://travis-ci.com/moodlehq/moodle-php-apache.svg?branch=7.0-jessie)](https://travis-ci.com/moodlehq/moodle-php-apache)|Jessie and PHP 7.0 EOL|
 | PHP 5.6      | Jessie  | 5.6-jessie       | [![Build Status](https://travis-ci.com/moodlehq/moodle-php-apache.svg?branch=5.6-jessie)](https://travis-ci.com/moodlehq/moodle-php-apache)|Jessie and PHP 5.6 EOL|
 
-# Example usage
+## Example usage
 The following command will expose the current working directory on port 8080:
 ```bash
 $ docker run --name web0 -p 8080:80  -v $PWD:/var/www/html moodlehq/moodle-php-apache:7.1
 ```
 
-# Features
-
+## Features
 * Preconfigured with all php extensions required for Moodle development and all database drivers
 * Serves wwroot configured at /var/www/html/
-* Verified by [automated tests](https://travis-ci.com/moodlehq/moodle-php-apache)
-
-# Directories
+* For PHP 7.3 and up, both `linux/amd64` and `linux/arm64` images are being built. Note that `linux/arm64` doesn't support the sqlsrv and oci extensions yet. Other than that, both architectures work exactly the same.
+* Verified by [automated tests](https://travis-ci.com/moodlehq/moodle-php-apache).
+* Autobuilt from GHA, on push.
 
+## Directories
 To faciliate testing and easy setup the following directories are created and owned by www-data by default:
+
 * `/var/www/moodledata`
 * `/var/www/phpunitdata`
 * `/var/www/behatdata`
 * `/var/www/behatfaildumps`
 
 
-# See also
+## See also
 This container is part of a set of containers for Moodle development, see also:
+
 * [moodle-docker](https://github.com/moodlehq/moodle-docker) a docker-composer based set of tools to get Moodle development running with zero configuration
 * [moodle-db-mssql](https://github.com/moodlehq/moodle-db-mssql) Microsoft SQL Server for Linux configured for Moodle development
 * [moodle-db-oracle](https://github.com/moodlehq/moodle-db-oracle) Oracle XE configured for Moodle development