Reduce the size of the initial backoff duration for web-hooks

What does this MR do and why?

Prior to this change, the initial backoff duration was 10 minutes, which was found to be suboptimal when the receiving endpoint suffers from large start-up latency and might be suspended during the initial backoff.

This change reduces the initial backoff to 1 minute.

See: https://gitlab.com/gitlab-org/gitlab/-/issues/37514, #375714 (closed)

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