New event delivery retry strategy

Starting from today, the events delivery retry strategy uses a base-2 exponential back-off (10s, 20s, 40s, 80s…), replacing the previous base-10 progression. This provides faster initial retries while still spacing out later attempts.

A new optional maximum wait time parameter can be configured per webhook. It sets an upper bound on the cumulated time an event will be retried from its first delivery attempt. When this duration is exceeded, the event is marked as failed regardless of the number of remaining retries. If not set, the existing behavior (retry until the number of retries is exhausted) is preserved.