www/{nginx,nginx-devel,freenginx}: 3rd-party modules management

Start moving the bundled 3rd-party modules into dedicated
nginx-module-* ports, so that module versions are maintained in a
single place instead of the GH_TUPLE lists of the nginx ports.

As a first step, convert www/nginx-module-lua into a hybrid port
that installs the lua-nginx-module sources next to the prebuilt
DSO and use them in the three nginx ports via an unversioned
BUILD_DEPENDS instead of fetching from GitHub.

Sponsored by: Netzkommune GmbH