add optional GeoIP2 module support

[tsautier]

Hello!

Feature request

Please consider adding optional GeoIP2 module support to the official nginx_proxy add-on.

Use case

The add-on already supports custom NGINX snippets via the customize options. This makes it possible to add custom directives under /share, but GeoIP2-based configuration cannot currently be used because the required NGINX module does not appear to be installed in the add-on image.

For example, a custom snippet that uses a variable such as $geoip2_data_country_code causes NGINX startup to fail with:

nginx: [emerg] unknown "geoip2_data_country_code" variable

Thx :)