Autofocus support in Ekos module for manualfocusdrive gphoto command for Nikon

Summary:
Improve Focus Module in Ekos by adding autofocus support for DSLR's that use manualfocusdrive command by gphoto instead of rel_focus_position for example, Nikon Z6 according to documentation http://www.gphoto.org/doc/remote/.
Nikon DSLR: Manual focusing only works in the "liveview" aka "preview" mode (with mirror up). In "non preview" mode the focus motor is only controllable by the autofocus engine. --set-config manualfocusdrive=step size

Test Plan:

1. Regression tests on the simulator for relative focus position
2. Test on Nikon Z6 and Nikon D 7100 for manualfocusdrive with iterative and polynominal algorithms.

Reviewers: KStars, mutlaqja

Reviewed By: KStars, mutlaqja

Subscribers: mutlaqja, kde-edu, zyziuk

Tags: KStars, KDE Edu

Differential Revision: https://phabricator.kde.org/D26314