Resource contents are written to logs on subscription failure

[epeartree]

Description
Upon hitting a subscription delivery failure, we currently log the failing payload which could be considered PHI. To avoid this risk we should avoid logging payloads.

To Reproduce
Steps to reproduce the behavior:

1. Create a SubscriptionDeliveringRestHookSubscriber;
2. Create and submit subscription with a non existing endpoint to simulate either network/connection failure;
3. Create a patient resource matching the subscription;
4. The resulting log will contain fields from the resource which could be considered PHI.

Expected behavior
Resource contents should not be written to logs on subscription failure.