Should OhttpDecapsulation or Hpke Errors be considered fatal

[benalleng]

At the moment it seems like OhttpDecapsulation errors and Hpke errors are considered fatal but in looking closer at them in #1843 I think that they can be transient but I would like some more brains on this.

[benalleng]

I have since dropped these changes from the PR as I figure we should answer this question first before making the change