Self-Diagnostics ( Error handling ) support

[lalitb]

As of now, the project is missing a consistent way of exposing errors / diagnostic information at sdk/exporter/processor level. We can use this Issue to discuss on whether/how to provide this.

Specification briefly talks about it:
https://github.com/open-telemetry/opentelemetry-specification/blob/609a63784b2da7d59efe2a39822a23b09ae5b637/specification/error-handling.md#self-diagnostics

How different projects are handling it:
.Net: https://github.com/open-telemetry/opentelemetry-dotnet/blob/master/src/OpenTelemetry/Internal/SelfDiagnostics.cs
Go: https://github.com/open-telemetry/opentelemetry-go/blob/5a728db2e9713b66615943129568834c5af86ff8/handler.go