Add metrics instrumentation for deprecated fields

[ketiko]

Is your feature request related to a problem? Please describe.
I would like to see if deprecated fields are being called in my API.

Describe the solution you'd like
I'd like to be able to use the existing metrics feature and log the number of times a deprecated field was called. This would allow me to graph it in Grafana and setup alerts before removing a field. I'd like it tagged by the operation/parent/field just like the other metrics. However this would just be a counter of fields with deprecation annotations.

Describe alternatives you've considered
I can always do this myself building a custom Instrumentation but thought it might be useful in the standard library.

I have a working example of this enhancing the existing MetricsInstrumentation class. But before I polished it up I wanted to see if it's something you'd like to add.

[oliemansm]

Think that might be a useful default instrumentation for others too. We welcome contributions, so feel free to create a PR to add this.

[narugoyal]

Hi @ketiko

I am also trying to introduce metrics for usage of deprecated fields. If possible, can you please share the working example.
Thanks in advance.