Python 3 based version

This ece2cmor3 v2.0.0 pre-release is the first python3 based version.

With that we are now at:

Python 3.11
CMOR 3.7.1
cdo 2.1.1

Especially in the genecec part the ordering of lists and dictionaries (and the unpinned ordering by xml.etree.ElementTree) have been handled such that the control output files stayed in the same order except for the request-overview files.

All files in the test-all case have been validated and show only at most rounding differences around precision.

A few wrap-up issues like #754, will be addressed in a next release.