Support for parameterless queryParams in JerseyUriBuilder

We have URIs encoded as `?key=value&flag&key2=value`, where you can see that `flag` has no value.

In the current implementation of `JerseyUriBuilder` these are not allowed

https://github.com/eclipse-ee4j/jersey/blob/3716939adb721351e01b78bc54845b97bb6c836d/core-common/src/main/java/org/glassfish/jersey/uri/internal/JerseyUriBuilder.java#L534-L544

We would like for Jersey to please support this feature, as it's frequently used by JS frontends as defined by rfc3986.