Add a default value filter.

Problem/Motivation

In some cases we get query parameters that are empty or have a value like "All" or "Any" which actually means the same that as if it wasn't there at all. In these cases, we would like to be able to remove the query parameters that meet these criteria so that we can use that version of the url for a canonical url.

Example:
https://example.com/get-involved/events?title=&field_location_borough_ci...

would become

https://example.com/get-involved/events?field_audience_target_id=30&fiel...

Note we removed title, field_location_borough_citywide_target_id and page.