Try to create two rpm, one for ngx with httpg patch, one for voms module

gitlab-ci and readme need to be updated

* Explicitly install build-time deps needed for this package
* Take the httpg patch from this repo

The debug spec file is not used, but let's keep it aligned with
the other one.

* Start from the upstream SPEC file.
* Use the %{name} macro instead of explicitly repeating openresty-voms
* Use system zlib, openssl and pcre dependencies and do not specify minimum
  versions
* Remove unused macros oroprefix, {zlib,pcre,openssl}_prefix
* The voms_module_prefix macro is assumed
* Mv-ing openresty binary in openresty-voms seems irrelevant
* Don't consider "tapset" files, they don't exist (any more)
* For debug builds use -Og
* Review the packaging script
  - Minimize the list of build-time packages to install
  - Set the voms_module_prefix macro in the .rpmmacros file. The prefix is
    on the command line, with a default
  - Build only the optimized RPM
* Start docker:dind with --tls=false to avoid timeouts during CI

Issue #17

Conflict is set against any version of openresty.