Web server should be migrated to NGINX

[loyeyoung]

Issue: The web server for the qwc-qgis-server should be migrated to NGINX.

Rationale:
qwc-qgis-server is the only container in the qwc-docker project that runs Apache rather than NGINX, per manisandro's comment here. Standardizing on one web server for the qwc-docker is the Right Thing for the reasons stated in this issue.

Implementation:

• Configuration instructions for NGINX are here.
• manisandro states that FastCGI is needed for the qgis-server. The QGIS Server Guide/Manual provides instructions for FastCGI implementation on NGINX.
• The QGIS Server Guide/Manual recommends the spawn-fcgi implementation for a production environment, for its efficiency and speed.
• Configuration instructions for spawn-fcgi are here.