Customer routes from template/plugin

[stefanwerfling]

Add new variables to nginx config or help over the ui:

Example:

proxy_set_header X-Plex-Client-Identifier $http_x_plex_client_identifier;
proxy_set_header X-Plex-Device $http_x_plex_device;
proxy_set_header X-Plex-Device-Name $http_x_plex_device_name;
proxy_set_header X-Plex-Platform $http_x_plex_platform;
proxy_set_header X-Plex-Platform-Version $http_x_plex_platform_version;
proxy_set_header X-Plex-Product $http_x_plex_product;
proxy_set_header X-Plex-Token $http_x_plex_token;
proxy_set_header X-Plex-Version $http_x_plex_version;
proxy_set_header X-Plex-Nocache $http_x_plex_nocache;
proxy_set_header X-Plex-Provides $http_x_plex_provides;
proxy_set_header X-Plex-Device-Vendor $http_x_plex_device_vendor;
proxy_set_header X-Plex-Model $http_x_plex_model;