Add REDIS_URL env if redis is enabled

[tkg61]

There is now a second redis url needed for multi-replica setting syncs:

https://github.com/open-webui/open-webui/blob/main/backend/open_webui/env.py

Need to update the workload template to add in the url for the new env if redis is enabled

[venkivijay]

Related issue on openwebui repo: open-webui/open-webui#10365

[chr0n1x]

for the time being can't we use .Values.extraEnvVars here?

[0xThresh]

Redis sub-chart has been removed due to Bitnami chart changes, this is no longer relevant.

[chr0n1x]

@0xThresh sorry if this was brought up somewhere else - I understand that the subchart was removed cause bitnami is 💩 . but we can still technically install our own redis instance (e.g.: roll our own, valkey, etc) and point openwebui @ that instead right? or does openwebui also no longer support redis as a whole?