Subscribe to new parcel notifications in PoWeb via Redis PubSub

[gnarea]

Describe the problem

We currently use NATS Streaming in PoWeb's collectParcels method to be notified about new parcels, but we're deprecating NATS Streaming in production (relaycorp/cloud-gateway#84).

Describe the solution you'd like

Replace the NATS Streaming-based non-durable subscription with one based on Redis PubSub, using node-redis or ioredis.

• Integrate Redis in development chart.
• Update publisher.
• Update subscriber.

Describe alternatives you've considered

Using GCP PubSub in Relaycorp-managed, production instances, whilst retaining NATS Streaming support (see #760). However, (1) we need Redis as a backing service anyway (see #19) and (2) making the underlying backend pluggable will increase complexity drastically.

Additional context

This isn't the only use of NATS Streaming. See #929

[github-actions]

🎉 This issue has been resolved in version 4.0.0 🎉

The release is available on:

• v4.0.0
• v4.0.0
• GitHub release

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