Request to add an option for case sensitivity in QNetworkRequest::setRawHeader().

Request to add an option for case sensitivity in QNetworkRequest::setRawHeader(), so it doesn't force header names to be converted to lowercase.

Currently, calling QNetworkRequest::setRawHeader("X-Api-Key", ...) results in the header name being converted to lowercase.

Some hardware devices have a legacy design that checks the case of the header name and does not match it if the case is changed.