[server] Support dynamic configuration for disk write-limit recover gap

[swuferhong]

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• I searched in the issues and found nothing similar.

Motivation

DiskUsageMonitor currently uses a hard-coded recover gap of 0.10 when
deciding when to recover from data disk write lock. This means writes only resume
after disk usage drops below server.data-disk.write-limit-ratio - 0.10, which
can be difficult to reach in practice.

We should make this recover gap configurable and dynamically updatable.

Solution

No response

Anything else?

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Willingness to contribute

• I'm willing to submit a PR!