Extend links in whitelist

Changes introduced

• Add the possibility that the following files can be added as links:
  • [0-9]{3}xxx/[0-9]{6}/*.py
  • [0-9]{3}xxx/[0-9]{6}/*/*.py
  • [0-9]{3}xxx/[0-9]{6}/*.dat excluding [0-9]{3}xxx/[0-9]{6}/*/*.dat

Tests

In the following the files MG_2.py, sample_2.dat and sample_2.py have been added as links in the 999999 directory. The CI recognises them correctly (except for sample_2.dat which is under 999999/MadGraphControl/, where the transform would not find it).

Also MG.py has been added as a link at the top level directory, which is also not allowed.

Issues resolved

Closes #