[Feature]: Align with Langflow to allow LANGFUSE_BASE_URL variable

[aimurphy]

Feature Area

Settings (configuration, model providers), Infrastructure (Docker, OpenSearch, Langflow)

Problem Description

Langfuse now provides LANGFUSE_BASE_URL instead of LANGFUSE_HOST.

In this PR, Langflow accepts LANGFUSE_BASE_URL or LANGFUSE_HOST.

OpenRAG should follow LF and accept either as well.

Proposed Solution

When configuring Langfuse tracing, OpenRAG should accept either LANGFLOW_BASE_URL or LANGFUSE_HOST.

Use Case

Users with existing Langfuse instances will be familiar with LANGFUSE_HOST.
Users with new Langfuse instances will expect LANGFUSE_BASE_URL and potentially be confused by LANGFUSE_HOST.

Alternatives Considered

No response

Priority

Nice to have

Additional Context

No response

Contribution

• I would be willing to help implement this feature.
• I can help test this feature once implemented.

Checklist

• I have searched existing issues and discussions to ensure this feature hasn't been requested before.