[otlp] UseOtlpExporter and AddOtlpExporter extensions don't play nice together

[CodeBlanch]

In 1.8.0 we introduced the UseOtlpExporter extension which will turn on OtlpExporter for all signals. If UseOtlpExporter is called more than once, or AddOtlpExporter is called in addition, exceptions will be thrown:

• NotSupportedException: Multiple calls to UseOtlpExporter on the same IServiceCollection are not supported.

  https://github.com/open-telemetry/opentelemetry-dotnet/blob/57c442cc7b2fe93c81ca877de28f5204fdb11ebb/src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Builder/OpenTelemetryBuilderServiceProviderExtensions.cs#L15

• NotSupportedException: Signal-specific AddOtlpExporter methods and the cross-cutting UseOtlpExporter method being invoked on the same IServiceCollection is not supported.

  https://github.com/open-telemetry/opentelemetry-dotnet/blob/57c442cc7b2fe93c81ca877de28f5204fdb11ebb/src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Builder/OpenTelemetryBuilderServiceProviderExtensions.cs#L24

This was intentionally done but some users have run into issues:

• https://github.com/dotnet/aspire/pull/3697#issuecomment-2058028632

Opening this issue to track the demand for changing the behavior.

[liammclennan]

See https://github.com/open-telemetry/opentelemetry-dotnet/issues/5537