Run through Gloo Mesh Enterprise docs for sanity

[willowmck]

No description provided.

[bgottfried91]

Ran through version 1.2.18 of the docs, setting up a management cluster and two data clusters using the Deploy Istio in Production page, Install Gloo Mesh Enterprise page, and Registering Clusters with Gloo Mesh page.

Didn't encounter any cases where I had to modify the given configs/steps except in the case of deploying Gloo Mesh Enterprise, where I had to modify the given values file slightly. Most of the modifications were because I was using auto-generated self-signed certs instead of pre-created certs, but the given values file currently doesn't deploy the metrics backend (metricsBackend.prometheus.enabled=false) - I'm assuming this is a mistake and that we'd want to deploy the metrics backend for a production install? Or is it set this way because it's assuming they'll be using an external Prometheus instance?