RSSI Controller std::thread memory leak

[PrimozLavric]

In rpr::Controller::start a thread is created using new, but never freed:
https://github.com/slaclab/rogue/blob/main/src/rogue/protocols/rssi/Controller.cpp#L146

Proposed fix:
Add delete thread_ to rpr::Controller::stop or better avoid creating a thread using new.

[bengineerd]

I created #866 to fix this.

Thank you for these reports. We appreciate contributions from external collaborators.

[bengineerd]

Resolved in #866.