1.0Performance: Add L1 aggregation flush period, which reduces the CPU load and helps young GC.
2. Replace do not direct send after the first aggregation to reduce the network #6400.
3. Enhance the DataCarrier to notify the consumer in no enqueue event in short term.
4. L1 aggregation flush period still works even no further metrics generated, powered by <3>
5. Fix gRPC remote client OOM. The concurrency control mechanism failed.
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