open-webui: Add Helm values; update chart to 18.0.0 (Open WebUI 0.13.0).

Chart 9+ prefixes object names with the release name, so pin the old
names with fullnameOverride to keep the existing PVC.  The pipelines
Deployment had to be recreated because its selector changed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Change-Id: Ia7fad5b7d9f7aa665bd26a203530863fe300b3c0
1 file changed