[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 or 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 contain…