## Problem
We saw the drain/fill operations not drain fast enough in ap-southeast.
## Summary of changes
These are some quick changes to speed it up:
* double reconcile concurrency - this is now half of the available
reconcile bandwidth
* reduce the waiter polling timeout - this way we can spawn new
reconciliations faster
## Problem
Background node operations take a long time for loaded nodes.
## Summary of changes
Increase number of concurrent reconciles an operation is allowed to
spawn.
This should make drain and fill operations faster and the new value is
still well below the total limit of concurrent reconciles.
## Problem
Pageserver restarts cause read availablity downtime for tenants. See
`Motivation` section in the
[RFC](https://github.com/neondatabase/neon/pull/7704).
## Summary of changes
* Introduce a new `NodeSchedulingPolicy`: `PauseForRestart`
* Implement the first take of drain and fill algorithms
* Add a node status endpoint which can be polled to figure out when an
operation is done
The implementation follows the RFC, so it might be useful to peek at it
as you're reviewing.
Since the PR is rather chunky, I've made sure all commits build (with
warnings), so you can
review by commit if you prefer that.
RFC: https://github.com/neondatabase/neon/pull/7704
Related https://github.com/neondatabase/neon/issues/7387
