[JUNGFRAU] Fix / DARK notebooks for JUNGFRAU and flip logic for do_relative_gain

This consists of

1. fix for JF Dark notebooks to run dark and plot for multiple modules.
2. Flipping the logic for do_relative_gain to relative_gain.

Description

1- Fix Dark notebook to run for multiple modules. 2- Flip the logic for Relative gain flag from no-relative_gain to relative_gain.

The motive behind these changes is to reduce the diffs for the next related MR at : https://git.xfel.eu/gitlab/detectors/pycalibration/merge_requests/518

How Has This Been Tested?

This was tested by running the notebook over multiple modules and comparing the results with the master.

Relevant Documents (optional)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Refactor

Checklist:

• My code follows the code style of this project.

Reviewers

@calibration