Add docs_uri_column_name to DatabricksRM

[chenmoneygithub]

As requested by Mosaic agent framework, we need to give users the flexibility to choose the column name for doc uri in order for agent framework to successfully render the trace. Previously we made a wrong assumption on the doc_uri format.

We will also do the following in the future:

• Remove the use_with_databricks_agent_framework flag and the logic branch.
• Move the Document conversion logic into MLflow.
• Delete the set_retriever_schema call.

This PR keeps it small to only unblock users, will have followup PRs for the other items.