issue: #43828
Implement robust rewatch mechanism to handle etcd connection failures
and node reconnection scenarios in DataCoord and QueryCoord, along with
heartbeat lag monitoring capabilities.
Changes include:
- Implement rewatchDataNodes/rewatchQueryNodes callbacks for etcd
reconnection scenarios
- Add idempotent rewatchNodes method to handle etcd session recovery
gracefully
- Add QueryCoordLastHeartbeatTimeStamp metric for monitoring node
heartbeat lag
- Clean up heartbeat metrics when nodes go down to prevent metric leaks
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Signed-off-by: Wei Liu <wei.liu@zilliz.com>
