Added documentation for Resource protection

[MaheshS08]

Purpose

This PR adds documentation for the resource protection mechanisms in Fluss: data disk write protection and KV leader replica capacity control. Both mechanisms were previously undocumented — the KV leader replica capacity feature was flagged as needing docs during review of #3614, and this PR follows the structure suggested in the linked issue to combine it with data disk write protection under a single "Resource Protection" page, leaving room for future protection mechanisms to be added alongside them.

Linked issue: close #3673

Brief change log

Addedwebsite/docs/maintenance/operations/resource-protection.mdwith two sections:

• Data Disk Write Protection — covers server.data-disk.write-limit-ratio, server.data-disk.write-recover-ratio, and server.data-disk.check-interval; the hysteresis behavior between the limit and recover ratios; the retriable DiskWriteLockedException error; the interaction with coordinator.offline-leader.retry-delay during leader election; and the diskUsageRatio / diskWriteLocked metrics.

• KV Leader Replica Capacity Protection — covers kv.leader-replica.memory-reserved; TabletServer resource reporting via tablet-server.advertised-resource.cpu-cores / tablet-server.advertised-resource.memory-size; how cluster-level capacity is calculated; the INSUFFICIENT_KV_LEADER_REPLICA_CAPACITY error; and the kvLeaderReplicaCount / kvLeaderReplicaCapacity metrics.

Tests

Documentation-only change; no code paths modified. No new tests required.

API and Format

No public API or config changes. No new config options were introduced — this PR documents existing options from #3340, #3612, #3539 and #3614.

Documentation

This PR is the documentation change described above.

[MaheshS08]

@wuchong , could you please review this PR !