ci: optional verbosity of license checker script

[tiborsimko]

Current behaviour

The license checker helper script output is rather verbose currently:

$ ./scripts/check_licenses.py
[INFO] Successfully validated file LHCb_2011_Beam3500GeV_VeloClosed_MagDown_RealData_Reco14_Stripping21r1_BHADRONCOMPLETEEVENT_DST.json
[INFO] Successfully validated file LHCb_2011_Beam3500GeV_VeloClosed_MagDown_RealData_Reco14_Stripping21r1_BHADRON_MDST.json
[INFO] Successfully validated file LHCb_2011_Beam3500GeV_VeloClosed_MagDown_RealData_Reco14_Stripping21r1_CHARMCOMPLETEEVENT_DST.json
[INFO] Successfully validated file LHCb_2011_Beam3500GeV_VeloClosed_MagDown_RealData_Reco14_Stripping21r1_CHARM_MDST.json
...
[INFO] Successfully validated file delphi-datasets-1999.json
[INFO] Successfully validated file lhcb-antimatter-matters-2017.json
[INFO] Successfully validated file delphi-datasets-1995.json
[INFO] Successfully validated file opera-detector-events-tau.json
[INFO] Processed 328 files within 1.86 seconds.
[INFO] Successfully validated 25203 records. No errors found.

This is unlike typical linting tools, such as flake8, markdownlint, etc, which are usually quiet by default.

Expected behaviour

Let's print out only "error" and "warning" type of messages by the license checker, so that it would behave similarly to other linting tools out there.

The script can allow user to increase verbosity (e.g. by means of a -v command-line option) if the user would like to see also the "info" type of messages and statistics about which files were processed, how much time the execution took, and how many values were validated in each file.