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.