Create rpm for OPA and NGINX

This PR creates RPMs for

• OPA, where the source is located in /etc/opa and the policy file must be shared with storm-tape
• NGINX configuration + NJS module located in /etc/nginx. The configuration is a template file that then produce a "storm.conf" file using a script and environment variables.

The RPMs are build and published on the Package Registry when one pushes a tag. The tag is expected to be like x.y.x, optionally with a leading v, and/or the build number like -q.

docker/Dockerfile.nginx

 FROM baltig.infn.it:4567/cnafsd/ngx_http_voms_module/nginx-httpg-voms:el9-latest
 
 COPY ./nginx/nginx.conf /etc/nginx/nginx.conf
-COPY ./nginx/storm.conf /etc/nginx/conf.d/storm.conf
+COPY ./nginx/assets/storm.conf.template /etc/nginx/templates/storm.conf.template
 COPY ./nginx/auth.js /etc/nginx/njs/auth.js
 
 CMD ["nginx", "-g", "daemon off;"]
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