Document load balancer requirements more clearly

[adrienthebo]

Gitpod services (specifically HTTPS and SSH) are exposed to the outside world via load balancers; however we don't document this dependency at a high level on the Gitpod installation prerequisites. In addition our reference architectures give brief setup instructions for load balancers but don't indicate specific requirements, such as EKS clusters requiring the use of either ELBs or a combination of ALB (for HTTPS when using AWS certificates) and NLB (for SSH).

This information should be presented at a high level in the requirements list and more detailed instructions should be presented in the reference architectures.

[lucasvaltl]

this is related to #10126