Fix Docker image to run in healthy mode

Refs https://redmine.teklia.com/issues/6470

• Use django-admin in Docker for easier deployments, as it's easier to setup worker commands or any other django-admin command than relying on ./manage.py
• Update healthcheck to verify /api/v1/corpus instead of /api/v1/public-key that is dependant on ponos
• Use $PORT in dockerfile
• Use arkindex script in dockerfile
• Warn on usage of ./manage.py
• Expose arkindex for developers too

Dockerfile

@@ -19,8 +19,8 @@ RUN chown -R ark:teklia /backend_static
 # Copy Version file
 COPY VERSION /etc/arkindex.version
 
-HEALTHCHECK --start-period=1m --interval=1m --timeout=5s \
-  CMD wget --spider --quiet http://localhost/api/v1/public-key/ || exit 1
+HEALTHCHECK --start-period=10s --interval=30s --timeout=5s \
+  CMD wget --spider --quiet http://localhost/api/v1/corpus/ || exit 1
 
 # Allow usage of django-admin by exposing our settings
 ENV DJANGO_SETTINGS_MODULE "arkindex.project.settings"