Make it possible to intercept the gRPC channel for OTLP based export

Is your feature request related to a problem?

I'm having trouble with a particular use of OTLP export, and it would have been helpful to be able to use gRPC channel interceptors as a debugging tool.

https://grpc-interceptor.readthedocs.io/en/latest/#client-interceptors

However, there is no way to pass down an interceptor into the OTLP gRPC exporter code.

Describe the solution you'd like

In the code here:
https://github.com/open-telemetry/opentelemetry-python/blob/main/exporter/opentelemetry-exporter-otlp-proto-grpc/src/opentelemetry/exporter/otlp/proto/grpc/exporter.py

A sketch of the logic might be something like:

+ def _default_interceptor(channel):
+  return channel

class OTLPExporterMixin(
   ...
   channel_options=...,
+ channel_interceptor=None):
+ channel_interceptor = channel_interceptor or _default_interceptor
...
+ self._channel = channel_interceptor(self._channel)
self._client = self._stub(self._channel)  # type: ignore [reportCallIssue]
...

Along with exposing access to channel_interceptor in the __init__ methods of the consuming classes (e.g. OTLPSpanExporter, OTLPMetricExporter, etc.)

Describe alternatives you've considered

No response

Additional Context

No response

Would you like to implement a fix?

None

Tip

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Start with exporter/opentelemetry-exporter-otlp-proto-grpc/src/opentelemetry/exporter/otlp/proto/grpc/exporter.py and trace how the channel is created and passed to the stub. Then inspect the init methods of consuming exporters such as OTLPSpanExporter and OTLPMetricExporter. Done means callers can provide a channel interceptor through those exporters and the interceptor is applied before the client stub is created.