Fetches the full documents of one municipality over all months (paging through the whole history) and returns the union of the field names found, with the first and last period in which each field appears. MI Social documents are sparse (a field only exists in the months it was published), which is why the whole history is scanned rather than a single document.
Value
A tibble with columns field, unit (inferred from the
suffix; "unknown" when the suffix does not say), storage_type,
in_dictionary, first_period and last_period. Empty, with a
warning, when the API has no document for the municipality.