Add MT parameters to the HA hook lib

This is the fifth ticket in the HA+MT effort. It covers the modifications of the HA hook parser to be able to support the new multi-threading related parameters, as described in the HA+MT design.

This will introduce the configuration parameters to HA. Technically, once #1732 (closed), #1733 (closed) and #1734 (closed) is done, this would be ready to use, but since there won't be the server component for it to handle multiple connections, it will have to wait for #1736 (closed).