OtlpGrpcMetricExporter::GetAggregationTemporality throws when the exporter is constructed with a shared grpc client

[dbarker]

Describe your environment
main branch at 57114c5

Steps to reproduce

1. Create a OtlpGrpcMetricExporter with a shared grpc client
2. Call GetAggregationTemporality

What is the expected behavior?
Returns the aggregation temporality for the exporter

What is the actual behavior?
A std::bad_function_call exception is thrown

Additional context

The aggregation_temporality_selector_ function object is not set by the constructor that accepts a shared grpc client (line 50).

Example stack trace: