Introduce new exporter helper with batching option

[dmitryax]

This is a tracking issue for introducing the new exporter helper and migrating the existing exporters to use it.

The primary reason for introducing the new exporter helper is to move the batching to the exporter side and deprecate the batch processor as part of making the delivery pipeline reliable, as reported in #7460. More details about moving batching to the exporter helper can be found in #4646.

Shifting batching to the exporter side grants us the opportunity to leverage the exporter's data model instead of relying on OTLP. As a result, we can achieve the following benefits:

• Ability to place failed requests back into the queue without the need for converting them back to OTLP format.
• Enhanced control in counting queue and batch sizes using basic items (like spans, data points, or log records for OTLP) tailored to different exporters, resolving the concern raised in issue Processor: Splitting summary metrics into timeseries. opentelemetry-collector-contrib#7134.
• Optional counting of queue and batch sizes in bytes of serialized data.

Adapting to the new exporter helper requires exporter developers to implement at least two functions:

1. Converter: to translate pdata Metrics/Traces/Logs into a user-defined Request.
2. Request sender: to send the user-defined Request

Design document: https://docs.google.com/document/d/1uxnn5rMHhCBLP1s8K0Pg_1mAs4gCeny8OWaYvWcuibs

(edit by @mx-psi) For essential sub-issues to mark this as complete see the 'Sub-issues' list below.

Additional sub-issues to get feature parity with the batch processor:

• [exporterhelper] Add an ability to batch by a key from pdata or context #10825

[bogdandrutu]

Some feedback about the interface:

1. [Traces|Metrics|Logs]Converter can be replaced with a simple func instead of having an interface. If you need in the future to extend capabilities of that, they can be options. Comparing interfaces with nil is problematic sometimes, see https://mangatmodi.medium.com/go-check-nil-interface-the-right-way-d142776edef1, referring to https://github.com/open-telemetry/opentelemetry-collector/blob/main/exporter/exporterhelper/metrics.go#L142
2. Can you make the old NewMetricsExporter to call into NewMetricsRequestExporter to remove duplicate code and to actually start testing the new path more intensively? Also removes lots of duplicate tests.

[dmitryax]

Thanks for the feedback!

Can you make the old NewMetricsExporter to call into NewMetricsRequestExporter to remove duplicate code and to actually start testing the new path more intensively? Also removes lots of duplicate tests.

That's what I wanted to do after #8248 is merged 👍