Mark operator docs as deprecated and update FAQ for choosing an installation method

[craigbox]

https://istio.io/latest/blog/2024/in-cluster-operator-deprecation-announcement/ means we need to mark the Operator docs as deprecated and update the FAQ to reflect such.

Regarding said FAQ, @bleggett writes

This FAQ needs a rework, the leadoff for istioctl is

The simplest and most qualified installation and management path with high security.

Which is

• not a useful or meaningful (or grammatically correct) sentence
• categorically false (there is absolutely no security advantage to installing with istioctl versus helm, it's exactly equivalent)

This is probably a vestige from the Helm 2 days, if I had to guess, which was deprecated like 6 years ago.

That FAQ should also either discourage the use of istioctl manifest generate or also mention helm template which does the same thing.