Use Case Guide: Setup mTLS to the application from NGF

[mpstefan]

As a user of NGF
I want a guide to help me understand how I can ensure all traffic that travels through NGF to my application is secured using mTLS
So that I can quickly secure my application's traffic within the cluster.

Acceptance

• Update existing BackendTLS doc to discuss how to enable mTLS using Gateway BackendTLS and BackendTLSPolicy.
• Add a diagram to show the interaction between Gateway and Service mTLS transaction
• Add yaml examples in the repository

[mpstefan]

As we cannot perform mTLS to the upstream at this time, added this to the backlog.

[nginx-bot]

Hi @mpstefan!

Thanks for opening this issue!
Be sure to check out our Contributing Guidelines and the Issue Lifecycle while you wait for someone on the team to take a look at this.