[server] Add resource-based KV leader replica capacity control

[swuferhong]

Purpose

Linked issue: close #3613

Add tabletServer resource reporting and a coordinator-side KvLeaderReplicaCapacityManager to protect clusters from creating too many KV leader replicas.

TabletServers now report optional CPU and memory information during registration. The coordinator derives kvLeaderReplicaCapacity from live tabletServer memory and kv.leader-replica.memory-reserved, tracks the current KV leader replica count in memory, rebuilds it on coordinator leadership startup, and checks/reserves capacity when creating KV tables or partitions.

The capacity limit is disabled unless more than half of live tablet servers report memory. Unknown-memory TabletServersuse the average known memory when the limit is enabled.

Also add dynamic config support, metrics, RPC error mapping, serde compatibility, auto-partition accounting, and tests for resource probing, capacity calculation, manual create/drop, and auto partition create/drop.

Brief change log

Tests

API and Format

Documentation

[beryllw]

Thanks for the change! One concern about rebuildCurrentCount(metadataManager) in dropDatabase: it rescans all databases/tables, but admin operations run concurrently on the coordinator. If another request drops a database mid-scan, listTables() throws DatabaseNotExistException, which propagates out and fails this dropDatabase request — even with ignoreIfNotExists=true.

This is what fails the Rust IT test_error_database_already_exist in CI: its drop_database(..., cascade=true) gets a DatabaseNotExist error for a different database (test_create_database) that a parallel test was dropping at the same time.