capture: set kafka partitioner to murmur2_random

[xvello]

Working on PostHog/posthog#21850 showed a discrepancy on the message key -> partition computation between python and rust. The issue is that rdkafka's default partitionner uses CRC32, that is not supported in python-kafka. Let's align on python's murmur2 partitionner (CPU overhead should be negligible).

Tested locally on a topic with 10 partitions, the same partition is used now.

[tiina303]

So this might shuffle keys around? we don't have noticable lag atm seems safe to ship

[bretthoerner]

So this might shuffle keys around? we don't have noticable lag atm seems safe to ship

It will, but it will shuffle them where they need to be anyway. :)

[xvello]

@tiina303 both PRs will indeed break ordering from both producers, to bring both producers into a third common place, where we expect them to agree on the partition.

I'll double-check processing lag before releasing both changes, as long as it's low the data risk seems acceptable