Section on running code checkers (pvs-studio, coverity etc...)

[luzpaz]

• Section on how to check coverity scans for FreeCAD
• Section on how to check pvs-studio scans for FreeCAD
• Section on how to trigger scans
• Implement automation for said scans (ATM @sasobadovinac is triggering them manually)

reference: FreeCAD/FreeCAD#11091 (comment)