feat(consumers): rust consumers quantized rebalance

[volokluev]

Add the ability to do quantized rebalancing for consumers, toggleable by runtime config.

What is quantized rebalancing?

Rebalancing events are synchronized to the tick of the clock. Controlled by the runtime config: quantized_rebalance_consumer_group_delay_secs__{consumer_group}

Let's say:

SET quantized_rebalance_consumer_group_delay_secs__spans=15

• When a consumer starts up: delay subscribing to a topic until timestamp % 15 == 0
• when a consumer gets a shutdown signal (ctrl-c): delay leaving the group until timestamp % 15 == 0

What else is in this PR?

This PR adds the ability to read from redis config directly. This was mostly done because I couldn't get the python bindings to work on my machine, it will still fall back to the old implementation if there is an error in the direct implementation

[john-z-yang]

Nit:
I had a little difficulty understanding this, it might be a little more easier to read if we do

let Ok(delay_secs) = runtime_config::get_str_config(...) else {
    return None;
}
delay_secs.parse().ok()

Or some variation to reduce nesting.

But this is on the aesthetic side of things

[john-z-yang]

Am I correct in assuming that this closure that is passed in runs in a separate thread, so the main loop is not blocked while it is sleeping before signaling shutdown?

[john-z-yang]

This seems reasonable to me, do we plan to have quantized rebalancing on the other end? I.e. Making the consumer wait a little bit before joining the consumer group