Create all.import_check.how_to_guide.md

[gpsaggese]

We have a docs/tools/all.import_check.reference.md that explains the inner working of the scripts. We want to have an how_to_guide according to ./docs/documentation_meta/all.diataxis.explanation.md The how-to should only contain examples of the typical uses.

It's ok to move stuff from reference to how-to to remove redundancy.

Let's clean up also the rest of the file and not only the part related to the new script

[ehaabbasil]

@gpsaggese Understood, will proceed accordingly.