[feature request] support extensible tag serialization

[djluck]

Package

OpenTelemetry.Exporter.OpenTelemetryProtocol

Is your feature request related to a problem?

It would be useful to better support the serialization of types not directly supported by the OTel protocol to tags.

Currently types not supported in TagWriter.TryWriteTag are converted to strings. While this is better than nothing, we loose opportunities to convert objects into rich key/ value pairs. Such an approach would lend itself well to supporting wide events as users would no-longer have to serialize objects to tags by hand and could instead rely upon library code to do this.

The motivation for such an enhancement is discussed here: #5718.
The difference between this issue and the prior linked issue is that instead of asking this project to build + support such a serializer, this issue asks that TagWriter is simply made to be extensible, in order to support any custom serialization of types not supported natively by Otel such as:

• MyObject
• List<MyObject>
• DateTime
• etc.

What is the expected behavior?

I would expect the changes might be of this form:

• A public interface is extracted from TagWriter
• A convenient way is provided to override the default TagWriter instance

Which alternative solutions or features have you considered?

The alternative is that you can provide an extension method to support serialization of unsupported objects. But this has several drawbacks around performance:

• Adding tags to Activity is relatively slow, due to casting/ boxing of structs and acquiring/ releasing the mutex that synchronizes adding tags
• Boxing of struct types to object incurs additional allocations
• Converting objects to strings ahead of time doesn't allow for the pooling of buffers, further increasing memory allocations

Additional context

No response