Add additional nginx sites configurations support

[medfreeman]

closes #786

Add a nginx_sites_conf array
to allow users to specify custom nginx confs to be templated to the server's
nginx/sites-available folder, that are then symlinked to nginx/sites-enabled.
Array element properties:

• src: jinja template path
• enabled: whether to enable / disable the site conf
  by symlinking it to nginx/sites-enabled / removing it (default true)

Default:

nginx_sites_confs:
  - src: no-default.conf.j2

Add nginx-sites playbook tag.

[swalkinshaw]

Looks great 👍

Thanks for the work and patience on this

[fullyint]

Works in my tests (and it unearthed #795 👍).
Thanks for this!

For the docs, yeah, I think some-name.conf.site.j2 is fine to suggest as a convention. You understood it all, that the child template convention of *.child is just to avoid the default templating to includes.d. People can use the convention or not. It is harmless to template extra files to includes.d that aren't part of the sitename subdirs.

[medfreeman]

Thanks to you both ! @fullyint i finally commited your code, i hope you don't mind !
Taking my time writing the doc, hope to be the clearest possible.

Next proposition in a week or two, have something like an 'external' or 'proxy' ssl setting / proxy conf to handle ssl termination.
Rationale: it needs changes in a lot of places, is hard to maintain, but again not sure if it warrants a PR or something more like a recipe

[fullyint]

Regarding SSL termination, the only prior discussion I recall was partial accommodation in #732. We ultimately figured child templates could handle the particular changes of #732, as implemented in "Child template example – complex."

[swalkinshaw]

Thanks 🚀