support v0.3.0 of configuration file format

[codeboten]

Is your feature request related to a problem?
I'm trying to load the current kitchen-sink example from the opentelemetry-configuration repository, but unfortunately I'm running into a problem setting headers for my OTLP exporter. This is the error I see

Invalid type for path "open_telemetry.tracer_provider.processors.1.batch.exporter.otlp.headers.0". Expected "scalar", but got "array".

It's caused by the change in headers format from a map to an array of name/value objects in open-telemetry/opentelemetry-configuration@f89f35a

Describe the solution you'd like
I would like to be able to use the following header configuration

    headers:
      - name: api-key
        value: "1234"

Describe alternatives you've considered
not using the latest file format, but that didn't work either because v0.3 is the only supported format :D

[brettmc]

Thanks for raising this. I've got a work-in-progress to implement the remaining features for 0.3 compatibility and I should have a PR ready in a couple of days...

[codeboten]

Thanks @brettmc!