Allow diagnostics to be published from a hardware_interface

[Timple]

Is your feature request related to a problem? Please describe.
For an actuator, often the actuator reports more values that just the measured one. For example current power consumed. It would be nice to have this information available on the /diagnostics topic.

Describe the solution you'd like
A way to easily supply diagnostics from a hardware_interface. For example:

hardware_interface::return_type MyActuator::read(const rclcpp::Time &, const rclcpp::Duration &);

hardware_interface::return_type MyActuator::write(const rclcpp::Time &, const rclcpp::Duration &);

hardware_interface::return_type MyActuator::produce_diagnostics(diagnostic_updater::DiagnosticStatusWrapper &stat);

Or:

hardware_interface::CallbackReturn on_configure(const rclcpp_lifecycle::State & previous_state);

hardware_interface::CallbackReturn add_diagnostic_task(const DiagnosticTask * t);

Describe alternatives you've considered
Creating a diagnostic_updater_ class member. Which also needs a node_ and then spin an executor. Like this: https://github.com/nicklgw/bdrive_hardware_interface/blob/f557bf1111f6ecc2df0389d25c7e73225e294a61/src/bdrive_hardware_interface.cpp#L93

Additional context