Allow JDBC Driver to pass HTTP header Key/Value pairs

Currently Beeline & ODBC driver does not support carrying user specified HTTP header.
The beeline JDBC driver in HTTP mode connection string is as
jdbc:hive2://<host>:<port>/<db>?hive.server2.transport.mode=http;hive.server2.thrift.http.path=<http_endpoint>,
When transport mode is http Beeline/ODBC driver should allow end user to send arbitrary HTTP Header name value pair.
All the beeline driver needs to do is to use the user specified name values and call the underlying HTTPClient API to set the header.
E.g the Beeline connection string could be jdbc:hive2://<host>:<port>/<db>?hive.server2.transport.mode=http;hive.server2.thrift.http.path=<http_endpoint>,http.header.name1=value1,
And the beeline will call underlying to set HTTP header to name1 and value1

This is required for the end user to send identity in a HTTP header down to Knox via beeline.