Preserve io.opentelemetry.exporter.otlp.logs.OtlpGrpcLogRecordExporterBuilder#setChannel and implement similar logic for HTTP

[vbedrosova]

We in JetBrains TeamCity are opentelemetry java sdk users and we require this method in our multi-node setup to have control over the executors in order to pass IO guard, etc.
Moreover we would appreciate similar ability for HTTP exporter as well as we can't support HTTP for our multi-node setup otherwise.

[jack-berg]

Preserving io.opentelemetry.exporter.otlp.logs.OtlpGrpcLogRecordExporterBuilder#setChannel is a duplicate of #4531.

I wonder if your use case would be satisfied if we were to expose a setExecuteService(ExecutorService) method on the OTLP exporter builders. Currently, the executor service is hardcoded for all implementations, but it seems reasonable to give callers control of this. WDYT?