[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.

  opentelemetry-dotnet/src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Builder/OpenTelemetryBuilderServiceProviderExtensions.cs

  Line 15 in 57c442c

  throw new NotSupportedException("Multiple calls to UseOtlpExporter on the same IServiceCollection are not supported.");

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

  opentelemetry-dotnet/src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Builder/OpenTelemetryBuilderServiceProviderExtensions.cs

  Line 24 in 57c442c

  throw new NotSupportedException("Signal-specific AddOtlpExporter methods and the cross-cutting UseOtlpExporter method being invoked on the same IServiceCollection is not supported.");

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

• Convert Seq component to use OTEL's AddProcessor instead of AddOtlpExporter dotnet/aspire#3697 (comment)

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

[liammclennan]

See #5537