Update `Histogram<T>` docs to note that `decimal` data will not be exported

### Describe the issue or suggestion

As per https://github.com/open-telemetry/opentelemetry-dotnet/issues/5615 when creating a `Histogram` the data will not acutally be exported.

Since the generic type param will accept a `decimal` it could be best to just add a second remark that when using it the data wont actualy be exported? Of course just removing `decimal` from the current list of types would also work.

Current Docs: https://learn.microsoft.com/en-us/dotnet/api/system.diagnostics.metrics.histogram-1

Happy to make a pull request doing the work however, I am not entirely sure what should be done.