ci: upload artifacts

[drzraf]

Build for multiple Nginx versions the way liboauth2 already did and also provides ready-to-use .so files (handy when a .deb package is restricted to only one)

Modeled after OpenIDC/liboauth2#62

[willstranton]

I'm not affiliated with this project, but have been trying to build this project from source for the last week. I kept getting core dumps when I added the .so file I was building. After stumbling on your pull request, I changed how I was doing the nginx ./configure with --with-compat like your change and it worked! Thank you!

[zandbelt]

I believe this better off living in its own repository, which would be an artifiact repository for ngx_openidc_module; I'd be happy to refer/link to it from the README/wiki

[drzraf]

I'm sorry @zandbelt I don't understand your answer nor the actual suggestion.

• Are you saying that precompiled shared object for NGinx aren't useful?
• Or that the CI shouldn't be involved into it?
• Or that it does suit this repository?
  (I tend to thing that these are actually useful, as part of the CI of this repository).

Then is it something else?
I don't understand the concept of "artifact repository" and its possible advantages.