[docs-metrics] Show AddView API using delegate

[CodeBlanch]

See: https://github.com/open-telemetry/opentelemetry-dotnet/pull/5554#issuecomment-2066915358

We should have some sort of advanced documentation which shows the AddView API which exposes a callback/delegate. The important part is strong wording that it isn't recommended to be used due to failures being swallowed at runtime and only written to self-diagnostic logging.

[devc007]

hey @CodeBlanch! I love to work on this but I don't know how to start.

[CodeBlanch]

@devc007

Let's add a section in here: https://github.com/open-telemetry/opentelemetry-dotnet/blob/main/docs/metrics/customizing-the-sdk/README.md

Something at the bottom. Like "Advanced scenarios" maybe?

Advanced scenarios

View configuration using delegate

The following code snippet shows how to use advanced selection criteria to customize the metrics output by the SDK. This requires the user to provide a Func<Instrument, MetricStreamConfiguration> which offers more flexibility in filtering the instruments to which the View should be applied.

[!CAUTION] It is not recommended to use the delegate overload of the AddView API because it is not evaluated until the process is running and a measurement is recorded. The OpenTelemetry SDK will NOT throw exceptions when running. Any mistakes made using this overload will cause the View to be ignored. Exceptions will be written to the internal logging only. Use this API with caution and only when the more simple overloads cannot be used instead.

[Content goes here]

For the content you could start by just restoring what we removed: https://github.com/open-telemetry/opentelemetry-dotnet/pull/5554/files#diff-425a8f436c341c05d10b76aac12d1295330116295a3556990ddf3d2bdaffdaecL43-L53

[geekrypter]

Hi @CodeBlanch, if this issue is not yet picked up, can I work on this?

[cijothomas]

Hi @CodeBlanch, if this issue is not yet picked up, can I work on this?

Yes please.