Feature: Support NO_AUTO_START and ALLOW_INTERACTIVE_AUTHORIZATION in dbus_proxy generated impls

Building on the previous work to support the no_reply attribute in dbus_proxy traits, I'd like to also be able to indicate that one or more of the other header flags should be included when building the messages in the generated code.

If my reading of the spec is correct, it doesn't look there is any need for additional handling of the request/reply messages; simply flipping the right bits in the header should be enough for both NO_AUTO_START and ALLOW_INTERACTIVE_AUTHORIZATION.

A WIP branch with a potential solution is here