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.