Add support in PTB for multiple sources

[ArBridgeman]

Summary

Some of our repositories -- like pyexasol, pytest-plugins -- have multiple source folders. The lint:security, lint:code, sonar:check should be expanded to allow multiple sources in the noxconfig > Config > source value. We should clarify that we would want the coverage lumped together in all of these cases or not, as pytest-plugins creates multiple python packages.