hooks for field comparison

[surajkota]

Is your feature request related to a problem?
Short term workaround to deal with server-side defaults by writing custom logic

3 patterns observed:

• Boolean fields returned as False. e.g.
  Scalable target in Applicationautoscaling - SuspendedState.DynamicScalingInSuspended returned as False by default
• String fields return default values. e.g. Model resource in SageMaker - PrimaryContainer.Mode retuned as SingleMode by default
• Slices have some extra fields returned from the server e.g. TODO

Describe the solution you'd like
pre and post nil check hook for comparison
or
hook to override the whole block of comparison logic for a field

Describe alternatives you've considered
Implement more algorithms like NilEqualsZeroValue but not going this route since the diff comparison logic is about to evolve/change