add: Info/Warning for setting up multi-instance setups

[Classic298]

Recently, many users were confused on why their kubernetes setup or multi-worker setup was not functioning properly.

I have decided to try to improve the docs in this regard.

• Adds info blocks to Redis environment variables, notifying the user of the need of setting these environment variables when trying to host Open WebUI in a multi-node/worker/instance environment
• Adds a warning block when choosing the kustomize quick-setup that informs the user to also set up the needed environment variables for scalable setups
• Adds a warning block when choosing the helm quick-setup that informs the user to also set up the needed environment variables for scalable setups

Relates to:
open-webui/open-webui#10365 (comment)

open-webui/open-webui#9032
open-webui/open-webui#12362
open-webui/open-webui#12286

[tjbck]

Thanks!