Introduce automated deploy to WP.org

Ported from 10up's GitHub Action: https://github.com/10up/actions-wordpress/blob/598b1572d5024340f09d7efc083a65ebff3bcdef/dotorg-plugin-deploy/entrypoint.sh

.gitlab-ci.yml

@@ -36,6 +36,7 @@ PHPunit:PHP7.2:MySQL:
     - phpunit
 
 PHPunit:PHP7.3:MySQL:
+  stage: test
   image: containers.ethitter.com:443/docker/images/php:7.3
   services:
     - mysql:5.6
@@ -46,6 +47,7 @@ PHPunit:PHP7.3:MySQL:
 
 PluginSVN:
   stage: deploy
+  image: containers.ethitter.com:443/docker/images/php:7.3
   before_script:
     - date
   script: ./bin/deploy.sh