Add application failure category

[THardy98]

What was changed

Added category to ApplicationFailure, users can now specify a category to signify the severity of their application failure. Application failure categories also map to different observability behaviours, namely, a BENIGN application failure downgrades log emissions to DEBUG for activity failures.

1. Closes [Feature Request] Apply application failure logging and metrics behaviour according to ApplicationErrorCategory #1672

2. How was this tested:
   small integration test

[mjameswh]

That's a pretty simple feature, but still, should probably add @experimental everywhere, just for safety.

[THardy98]

That's a pretty simple feature, but still, should probably add @experimental everywhere, just for safety.

added experimental to the category enum docstring

[mjameswh]

Great, thanks!