opentelemetry-exporter-otlp-proto-grpc: set user agent properly

It looks like metadata is ignored and instead we should set the
grpc.primary_user_agent channel option instead. User-agent will change
from:
grpc-python/1.71.0 grpc-c/46.0.0 (linux; chttp2)

to:
OTel-OTLP-Exporter-Python/1.34.1 grpc-python/1.71.0 grpc-c/46.0.0 (linux; chttp2)

Author: xrmx

exporter/opentelemetry-exporter-otlp-proto-grpc/src/opentelemetry/exporter/otlp/proto/grpc/__init__.py

@@ -73,4 +73,6 @@
 from .version import __version__
 
 _USER_AGENT_HEADER_VALUE = "OTel-OTLP-Exporter-Python/" + __version__
-_OTLP_GRPC_HEADERS = [("user-agent", _USER_AGENT_HEADER_VALUE)]
+_OTLP_GRPC_CHANNEL_OPTIONS = [
+    ("grpc.primary_user_agent", _USER_AGENT_HEADER_VALUE)
+]

exporter/opentelemetry-exporter-otlp-proto-grpc/src/opentelemetry/exporter/otlp/proto/grpc/exporter.py

@@ -51,7 +51,7 @@
     _get_resource_data,
 )
 from opentelemetry.exporter.otlp.proto.grpc import (
-    _OTLP_GRPC_HEADERS,
+    _OTLP_GRPC_CHANNEL_OPTIONS,
 )
 from opentelemetry.proto.common.v1.common_pb2 import (  # noqa: F401
     AnyValue,
@@ -196,6 +196,7 @@ class OTLPExporterMixin(
         headers: Headers to send when exporting
         timeout: Backend request timeout in seconds
         compression: gRPC compression method to use
+        channel_options: gRPC channel options
     """
 
     def __init__(
@@ -208,6 +209,7 @@ def __init__(
         ] = None,
         timeout: Optional[float] = None,
         compression: Optional[Compression] = None,
+        channel_options: Optional[TypingSequence[Tuple[str, str]]] = None,
     ):
         super().__init__()
 
@@ -238,10 +240,10 @@ def __init__(
             self._headers = tuple(temp_headers.items())
         elif isinstance(self._headers, dict):
             self._headers = tuple(self._headers.items())
-        if self._headers is None:
-            self._headers = tuple(_OTLP_GRPC_HEADERS)
-        else:
-            self._headers = tuple(self._headers) + tuple(_OTLP_GRPC_HEADERS)
+
+        self._channel_options = channel_options or tuple(
+            _OTLP_GRPC_CHANNEL_OPTIONS
+        )
 
         self._timeout = timeout or float(
             environ.get(OTEL_EXPORTER_OTLP_TIMEOUT, 10)
@@ -258,6 +260,7 @@ def __init__(
             self._channel = insecure_channel(
                 self._endpoint,
                 compression=compression,
+                options=channel_options,
             )
         else:
             credentials = _get_credentials(
@@ -270,6 +273,7 @@ def __init__(
                 self._endpoint,
                 credentials,
                 compression=compression,
+                options=channel_options,
             )
         self._client = self._stub(self._channel)