Querying for metadata fields and values present in the index

I would like to query my index to simply return a list of all the unique metadata field names and corresponding values that currently exist for all the vectors in the index. If it matters, for my index this would return less than 5 unique metadata fields and less than 10 unique values for each field, so it’s not a huge number.

What would the python query be to accomplish this?

Is this not as straightforward as I expected it would be?