Add code to handle new `breakdown_labels` param metadata option

[anth-volk]

Some US params are deeply nested and include range(x,y) values that prevent logical naming using the metadata structures that we already have. PolicyEngine/policyengine-us#7126 adds a new breakdown_labels entry that accepts a list of values that correlate with each tier of a given nested param. We should modify .py to apply those breakdown_labels automatically to each nested tier.