Make RetryReason.allowsNonIdempotentRetry() public

The Couchbase docs say:

You can check if a request is idempotent through the idempotent() getter, and also check if the RetryReason allows for non-idempotent retry through the allowsNonIdempotentRetry() getter

But RetryReason.allowsNonIdempotentRetry() is package protected, making it difficult to call from user code.

Suggested release note text: RetryReason.allowsNonIdempotentRetry() is now public, so you can call it from a custom RetryStrategy.