Fixes #5808: Handle missing techniques with active techniques in trees

The goal is to let the user have a chance to actually be able to generate policies, even if a technique was removed from the git repos but still have active techniques. 

=> correct displaying of active techniques in directive/technique trees in that case, 
=> on the technique library management screen, disable active technique with missing techniques. 
the name of the service is the worst ever
rwActiveTechniqueRepository = RudderConfig.woDirectiveRepository

it took me a while to understand how to "disable" a technique