Fix calibration (backport #1017)

[mergify]

It seems that for certain robots the calibration extraction and correction fails. This PR aims at fixing this.

ToDo:

• Add a test showing that some calibrations don't get corrected correctly
• Fix the code (We have a fix already, locally, I just need to clean it up)
• Add more documentation on the algorithm (It took me way too long to understand my old code...)
• Also backport things to ROS 1 (Fix calibration Universal_Robots_ROS_Driver#704)

  ---

  This is an automatic backport of pull request Fix calibration #1017 done by Mergify.

[mergify]

Cherry-pick of 557b57e has failed:

On branch mergify/bp/iron/pr-1017
Your branch is up to date with 'origin/iron'.

You are currently cherry-picking commit 557b57e.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   .pre-commit-config.yaml
	new file:   ur_calibration/doc/algorithm.rst
	new file:   ur_calibration/doc/calibration_example.png
	new file:   ur_calibration/doc/calibration_example_corrected.png
	new file:   ur_calibration/doc/calibration_uncorrected.png
	new file:   ur_calibration/doc/conf.py
	new file:   ur_calibration/doc/usage.rst
	modified:   ur_calibration/src/calibration.cpp
	modified:   ur_calibration/test/calibration_test.cpp

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   ur_calibration/doc/index.rst

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[fmauch]

This seems fine. Conflict resolving automatically produced the correct result.