Support diffForStages and failOnDestructiveChanges

[mrgrain]

This is basically the inverse of the current noDiffForStages and noFailOnDestructiveChanges.

But that's probably just one solution to my actual use case:

• I have a large app with many stacks/stages across different regions
• For reasons, I cannot have a single role that can perform diff for all stages across all regions
• I am looking for a way to group my stacks into multiple jobs that each use a different role and diff a subset of stages
• Currently I have to exclude the unwanted stages, which causes a lot of repetition.

PS: Not using failOnDestructiveChanges. Just threw this in for good measure. 😂

[bnazanb]

noDiffForStages doesn't even seem to work. Based on code, we get the input, but not doing anything with it.