[exporterhelper] Move batching API to a separate module

[mx-psi]

We can look into separating the batching API into a different module. This helps in the separation of concerns and potentially allows us to stabilize exporterhelper without stabilizing the batching API.

[mx-psi]

The symbols that would be moved to a different module would be those that are marked with Experimental/early stage of development, that is:

• BatcherOption
• WithRequestBatchFuncs
• WithBatcher
• WithRequestQueue
• Request
• RequestErrorHandler
• RequestFromLogsFunc, RequestFromMetricsFunc, RequestFromTracesFunc

We would also move the exporterqueue and exporterbatcher packages into this separate module.