Grpc service accounts

[sodomelle]

It seems like gRPC sets the audience and scope options based on the gRPC service name, so they can't be set in the config.

Example usage:

destination {
    google-pubsub-grpc(
        project("test")
        topic("test")
        auth(service-account(key ("path_to_service_account_key.json")))
    );
};

[github-actions]

This Pull Request introduces config grammar changes

axoflow/62228cd45e7744ded91a839c6893c8b2835c50f5 -> sodomelle/grpc-service-accounts

--- a/destination
+++ b/destination

 axosyslog-otlp(
     auth(
+        service-account(
+            <empty>
+            key(<path>)
+            token-validity-duration(<number>)
+        )
     )
 )

 bigquery(
     auth(
+        service-account(
+            <empty>
+            key(<path>)
+            token-validity-duration(<number>)
+        )
     )
 )

 clickhouse(
     auth(
+        service-account(
+            <empty>
+            key(<path>)
+            token-validity-duration(<number>)
+        )
     )
 )

 google-pubsub-grpc(
     auth(
+        service-account(
+            <empty>
+            key(<path>)
+            token-validity-duration(<number>)
+        )
     )
 )

 loki(
     auth(
+        service-account(
+            <empty>
+            key(<path>)
+            token-validity-duration(<number>)
+        )
     )
 )

 opentelemetry(
     auth(
+        service-account(
+            <empty>
+            key(<path>)
+            token-validity-duration(<number>)
+        )
     )
 )

 syslog-ng-otlp(
     auth(
+        service-account(
+            <empty>
+            key(<path>)
+            token-validity-duration(<number>)
+        )
     )
 )

[alltilla]

2 minor news entry related comments, otherwise approve!

[alltilla]

macOS is failing on main, too, it is not caused by this PR.