The typed value slot of a project-level (user-submitted) search parameter,
matching the fixed dynamic_parameters.value.* schema declared in the
Elasticsearch mapping. Exactly one field is set, matching the parameter’s
SearchParamType. Unlike system-level parameters, a user-submitted
parameter’s URL is arbitrary and can’t safely become an Elasticsearch
field name (mapping explosion, plus Elasticsearch would silently collapse
any dot in that URL into a nested object path) - so it’s stored as the
plain string value of the url field instead. See DynamicParameterEntry.