Index metadata does not change after add_to_index or delete_from_index

After I built an index, I thought I was being clever by reading in `docid_metadata_map.json` to be able to review metadata and select documents I want to work with. However, when adding (`add_to_index`) or removing (`delete_from_index`) from the index, it appears that while the operations seem successful, the `docid_metadata_map.json` and `pid_docid_map.json` files are not updated.

Is this expected behavior? I'd think we'd want to have those files updated to allow for effective metadata management.

Thanks for any insights.

Start by tracing the add_to_index and delete_from_index entry points and how they handle docid_metadata_map.json and pid_docid_map.json. Verify whether each operation updates both files and define done as keeping the metadata files consistent with the index after additions and removals.

Written by the indexing model from the issue text.