NH-82238 Don't inject baggage header if empty

[tammy-baylis-swi]

In SW propagator inject method for outgoing requests, do not re-inject baggage header if value is empty, i.e. if "baggage": ""

I think technically "baggage": "" is allowed according to HTTP RFC 7230 section 3.2 where

field-value = *( field-content / obs-fold )

and

HTTP does not place a predefined limit on the length of each header field or on the length of the header section as a whole

The W3C Candidate Recommendation for Baggage does not explicitly mention a separate header length requirement.

For the W3C Recommendation for tracestate, it says this, which is not for Baggage but seems like a good guide for not continuing baggage propagation if empty:

Empty and whitespace-only list members are allowed. Vendors MUST accept empty tracestate headers but SHOULD avoid sending them. Empty list members are allowed in tracestate because it is difficult for a vendor to recognize the empty value when multiple tracestate headers are sent. Whitespace characters are allowed for a similar reason, as some vendors automatically inject whitespace after a comma separator, even in the case of an empty header.

[cheempz]

LGTM!