[feature]: Update documentation to detail how to put Plane behind existing Nginx proxy for Plane self-hosted

Is there an existing issue for this?

• I have searched the existing issues

Summary

Please provide documentation and changes (Nginx site template at least) to plane self-hosted detailing how to setup an external Nginx instance to act as reverse proxy for Plane self-hosted.

Why should this be worked on?

Plane self-hosted is so fantastically easy, providing Plane in all it's glory in a close to a single command on the NGINX_PORT.
Documentation, templates, and any changes required to Plane to enable the self-hosted Plane to be integrated into an existing environment would further increase usability.
For example, being able to provide Plane self-hosted on my existing FQDN or IP such as https://fqdn.blah/plane or http://192.168.1.10/plane with minimal fuss would be ideal.
Additionally, providing SSL on Plane is most elegantly done via an external (to Plane self-hosted) Nginx (or other) reverse proxy which is configured to serve HTTPS content.

MVP should be:

• A section in the self-hosted README either containing the info or a link to a separate piece of documentation.
• An Nginx template that can be placed, largely verbatim, into the likes of /etc/nginx/sites-enabled.
• Additional changes required for this to work on both FQDN and IP.
• Profit.