Make checks_output_dir argument optional for lb-ap check command
Makes the argmuent checks_output_dir
for the lb-ap check
command optional. This is the argument that defines where the output from the check will be stored. If unspecified, it will be stored in a "checks" directory in the same location as the ntuple specified for the test_ntuple_path
argument.
This resolves #8 (closed)
Work related to https://gitlab.cern.ch/lhcb-dpa/project/-/issues/93