HttpClient that has been assigned or has been used by this object.
The life cycle might not be or might be tied to this object, depending on
whether HttpClient was passed to or created by this object
Assign an HttpClient that this object should use. The life cycle
of the given HttpClient is independent of this object. Closing or
shutting down this object does not have any impact on the given client.
Callers must ensure that the given client is properly closed elsewhere.