Make it possible to downscale even if group downscale enabled but not both reads and writes need to be downscaled

[Jofen]

The issues I've seen is when I set "always-decrease-rw-together" to true, if for example, writes needs to be downscaled but reads is not. The tool would ignore the downscale operation of writes and wait until both writes and reads can be downscaled. That could possibly never happen and therefore writes would never get downscaled.

I am thinking to add a "timeout-interval" config that works in conjunction with the "always-decrease-rw-together" config. That is, if a downscale needed but can't decrease rw together at that time, the downscale operation would be queued, and if it's been queued for a long time that exceed the timeout interval, then it should just apply that single read or write downscale.

[gretel]

@sebdah, what's your opinion on this? regards

[sebdah]

I haven't heard many people that need it. But it's a good feature and I'd be likely to merge a PR for this.

[WalkerCodeRanger]

I want to second this. In particular, if one isn't scaling down because it has already reached its minimum, then that should never block the scale down of the other.