Feat loadbalancing exporter support batch

[pp861]

Description: <Describe what has changed.>

The performance of loadbalancing exporter is very poor when stress testing，even if use the batch processor. this is due to loadbalancing exporter split traces data to exactly single trace, and calculate backend endpoint by traceID, and then expose trace data one by one using otlp exporter. In order to improve the throughput, I add a batch mode, If you care about performance，you can enbale it like this：

exporters: loadbalancing: protocol: otlp: timeout: 2s resolver: static: hostnames: - endpoint-1:55678 - endpoint-2:55678 batch: enable: true timeout: 200ms send_batch_size: 8192

Link to tracking Issue: <Issue number if applicable>

Testing: <Describe what testing was performed and which tests were added.>

Documentation: <Describe the documentation added.>

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