[bug fix]Fix community_report config doesn't work in settings.yaml

[KylinMountain]

Description

The community_report in settings.yaml doesn't work. Actually, it is community_reports in the code instead of community_report.

Related Issues

https://github.com/microsoft/graphrag/issues/379

Proposed Changes

Update the field in settings.yaml template to community_reports. Update the related env filed to community_reports to align the code.

Checklist

• [x] I have tested these changes locally.
• [x] I have reviewed the code changes.
• [x] I have updated the documentation (if necessary).
• [x] I have added appropriate unit tests (if applicable).

Additional Notes

[Add any additional notes or context that may be helpful for the reviewer(s).]