Adjusting nginx rewrite rules to avoid sync issues when using a different port or non-ssl setups.

[pmaldera]

This PR aims to fix sync issues linked to the default nginx config when using a different port than 80 or non-ssl setups (local network test or home-only usage).

I encountered sync issues when testing calendar syncs iOS in two situations:

• When I changed the exposed port to one different from 80 using docker port mapping, which caused a redirection issue because the port is not kept in the redirection therefore attempting to reach the default http(s) port (fixed with the $http_host variable).
  • Latest issue about port redirection
  • Issue about using a different port
  • Possibly related issue
• When the setup is not using a domain or ssl (for example for a local network usage at home) sync issues can happen because of a http to https rewrite by the system/software used (fixed with the $scheme variable).
  • Some issue I stumbled upon when debugging
  • Related issue