Document TLS Configuration for Agent Communication

[mpstefan]

As a user of NGF in a production environment
I want a guide to explain to me how to replace the self-signed certs for Agent communication in my production environment
So that I can keep my production environment secure.

Acceptance

• A guide is added under the installation section of the NGF documentation that outlines how to integrate cert-manager to replace self-signed certificates for Agent communication.
• The existing installation docs, in the "before you begin" section, include a note that makes the user aware of the self-signed certs and links to the guide to replace them.