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/files/usr/local/etc/php-fpm.d/php-fpm.conf

@@ -1,15 +1,21 @@
 [global]
 daemonize = no
+error_log = /dev/stderr
+log_buffering = no
 
 [default]
-listen = /tmp/php-fpm.sock
+listen = 9000
+user = www-data
+listen.owner = www-data
+listen.group = www-data
 pm = ondemand
 pm.max_children = 30
 pm.process_idle_timeout = 10s
 pm.max_requests = 500
 catch_workers_output = yes
+decorate_workers_output = no
 chdir = /
-php_admin_value[error_log] = /tmp/php_error.log
+pm.status_path = /status
 php_admin_value[log_errors] = On
 php_admin_value[expose_php] = Off
 php_admin_value[display_errors] = Off