pubsub: expose a maxDurationPerAckExtension setting for subscribers

[hongalex]

For languages that support lease management, we have bound the percentile distribution to 10s - 10m. It would be useful if the upper bound were configurable.

A user might process messages very slowly (8m to ack)
If the application fails 5s after receiving a message (whose ack deadline was set to 8m, because that's the deadline the percentile distribution gave), the user has to wait 7m55s for the message to be redelivered
Users should be able to set maxDurationPerAckExtension = 20s, which caps an individual modAck RPC to 20s. This would have the downside of causing more modack RPCs to be sent, but the upside that the redelivery time would only be 15s
This setting differs from maxExtensionMinutes, which defines the total amount of time we'll hold a message.

maxDurationPerAckExtension should be disabled if set to be 0 (or less), and should default to 0.

For an idea of how this is implemented, please refer to the Go implementation, Github PR.

[hongalex]

From a discussion from the previous maintainer, it seems like the percentile distribution is only used when ackDeadline is not set. This is inconsistent with the other languages, so this might need to be removed at a later point (possibly bundled with another breaking change).

[feywind]

Moving to internal backlog.

[hongalex]

This is now exposed as SubscriberOptions.maxAckDeadline and corresponding minAckDeadline

nodejs-pubsub/src/subscriber.ts

Lines 575 to 576 in 08d00a1

	minAckDeadline?: Duration;
	maxAckDeadline?: Duration;