### What problem does this PR solve?
Dockerfile v0.25.0 expects nginx conf at path
/etc/nginx/ragflow.conf.python, see
[Dockerfile#L200](ca01c7a745/Dockerfile (L200))
However current helm template mount the conf at path
/etc/nginx/ragflow.conf causing runtime error at startup time.
### Type of change
- [X] Bug Fix (non-breaking change which fixes an issue)
---------
Co-authored-by: Mauro Gattari <mauro.gattari@infn.it>
### What problem does this PR solve?
_Briefly describe what this PR aims to solve. Include background context
that will help reviewers understand the purpose of the PR._
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
For helm deployment, there is also requirement to enable the Admin
Service for administrative operations.
So expose the ability of enable/disable this function by helm
configuration.
When it's enabled (by default),
<img width="486" height="190" alt="image"
src="https://github.com/user-attachments/assets/4db0dc3d-bd94-4ad9-bb5d-a240aac5e1c5"
/>
Admin access and operations would be feasible like below,
<img width="2530" height="876" alt="image"
src="https://github.com/user-attachments/assets/3e948e1b-7522-4f8d-8dc0-c80a22242022"
/>
Something like 'user management' is very much important for Ragflow
User/Owner to control their clients.
### What problem does this PR solve?
Add's a Helm chart for deploying RAGFlow on Kubernetes.
Closes#864.
### Type of change
- [X] New Feature (non-breaking change which adds functionality)
