Allow streams to opt into less consistent writes for high throughput

[ripienaar]

Proposed change

Streams do a lot of consistency checks on each publish - ensuring that the message hit a disk on the quorum before marking it as accepted. This comes at a huge cost in performance.

We should allow a stream to opt-in to a less strict mode favouring throughput which could relax some consistency checks.

JetStream used to have this as the primary model for writes early on but this was moved to a more strict model, the old code is still there and we can revive that under a opt-in flag

Use case

Fast publishers might be ok with lesser consistency models for data where some being lost is not a problem. Combined with Batch Publishes (#6549) this could allow for very high throughput use cases

Contribution

No response