Automate version selection for SLC

[MarleneKress79789]

Currently the user specifies which version of the slc they want to download. this leads to potentially downloading incompatible slc's. instead the code should automatically download the slc with the same version as the installes TE package.

• check which package version is installed
• • https://docs.python.org/3.8/library/importlib.metadata.html#distribution-versions
• • or create automatic version.py file and check that
• set as version for the slc before the download
• allow overriding this version for emergencies
• don't mention the override in the user guide but do mention in the dev guide
• make sure the version parameter does not show up in user guide or cli help , probably by using an environment variable
• what to do about testing before release/right after release?