### What problem does this PR solve?
This PR fixes two issues in the OpenDAL storage connector:
1. The `health` method was missing, which prevented health checks on
the storage backend.
3. The initialization of the `opendal.Operator` object included a
redundant scheme parameter, causing unnecessary duplication and
potential confusion.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
### Background
- The absence of a `health` method made it difficult to verify the
availability and reliability of the storage service.
- Initializing `opendal.Operator` with both `self._scheme` and
unpacked `**self._kwargs` could lead to errors or unexpected behavior
if the scheme was already included in the kwargs.
### What is changed and how it works?
- Adds a `health` method that writes a test file to verify storage
availability.
- Removes the duplicate scheme parameter from the `opendal.Operator`
initialization to ensure clarity and prevent conflicts.
before:
<img width="762" alt="企业微信截图_46be646f-2e99-4e5e-be67-b1483426e77c"
src="https://github.com/user-attachments/assets/acecbb8c-4810-457f-8342-6355148551ba"
/>
<img width="767" alt="image"
src="https://github.com/user-attachments/assets/147cd5a2-dde3-466b-a9c1-d1d4f0819e5d"
/>
after:
<img width="1123" alt="企业微信截图_09d62997-8908-4985-b89f-7a78b5da55ac"
src="https://github.com/user-attachments/assets/97dc88c9-0f4e-4d77-88b3-cd818e8da046"
/>
### What problem does this PR solve?
This PR resolves the inconsistency in the opendal configuration where
both `schema` and `scheme` were used as keys. The code and
configuration file now consistently use `scheme`, which helps prevent
configuration errors and runtime issues. This change improves code
clarity and maintainability.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
### Additional context
- Updated both `conf/service_conf.yaml` and
`rag/utils/opendal_conn.py` to use `scheme` instead of `schema`
- No breaking changes to other configuration fields
### What problem does this PR solve?
#8074
Oss support opendal(including mysql)
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
---------
Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>
