Enhancement: Add Docker Hub image (#965)

* Enhancement: Add Docker Hub image

* Push to ghcr.io

* Add all `org.opencontainers.image.xxx` labels using `--label` instead of `LABEL`

* Change `php-fpm` to listen on `:9000` to expose prometheus metrics via `php-fpm_exporter`

* Include `yarn.lock` to speed up builds

* Reorder

* Use correct sha for pr

* Add logging before overriding values in config

* Add `DEBUG=true` env var for verbose `entrypoint.sh` logs

* Print php exception when snappymail fails to generate data directory and config file on the very first time

* Log snappymail version

* Fix COPY statement

* Add .dockerignore

* Add `USER` and `ENTRYPOINT`

* Update `.dockerignore`

* Add docker image test

* Push only if image test succeeds

* Log when startup is successful

* Use plain `docker build` in `build_and_test.sh`

* Fix test output

.docker/release/test/test.sh

@@ -0,0 +1,10 @@
+#!/bin/sh
+# This script tests a given docker image using https://github.com/GoogleContainerTools/container-structure-test
+set -eu
+SCRIPT_DIR=$( cd "$(dirname "$0")" && pwd )
+IMAGE=${1:-}
+echo "Testing image: $IMAGE"
+docker run --rm -i \
+    -v /var/run/docker.sock:/var/run/docker.sock:ro \
+    -v "$SCRIPT_DIR/config.yaml:/config.yaml:ro" \
+    gcr.io/gcp-runtimes/container-structure-test:latest test --image "$IMAGE" --config config.yaml