get https://api.productboard.com/hierarchy-entities/custom-fields
Returns detail of all custom field definitions. This API only returns the data regarding the custom field definition, not the values for hierarchy entities. Values are managed by Custom Fields Values endpoints.
When listing, the type filter has to be specified to allow us to add new types without breaking existing clients. It's possible to specify multiple types in the filter.
This API is paginated, only the first 100 items are returned by default. The client should then recursively follow links.next link in the response to fetch the next page.