Validate that the metadata is always a dict

[npatki]

Problem Description

The diagnostic and quality reports always expect that the metadata is a dictionary. This can be confusing because in other libraries (such as the SDV), the metadata is actually its own object.

Expected behavior

If I don't pass in a dictionary into a report, provide a helpful error message.

from sdmetrics.reports.single_table import DiagnosticReport

report = DiagnosticReport()
report.generate(real_data, synthetic_data, metadata_object)

InvalidInputError: The provided metadata is not a dictionary.

Additional context

We cannot use metadata objects in SDMetrics because we are not using or importing the SDV.