Add support for open telemetry collectors

[DaniTulp]

To add support for more tracing back-ends it would be great if benthos could support OpenTelemetry collectors. It would allow services like datadog (which is of interest for me 😛 ) or any other open telemetry collector to be used.

An example implementation of multiple collectors can be found here. In this example there are multiple collectors used over grpc, but there's also support for http. I'm not sure if there are any other standards that are supported.

From what I've gathered by looking at the jaeger implementation it looks fairly similar.

Proposed minimal api

The below implementation should allow benthos to add support for multiple collectors over multiple protocols. This might miss some fields (or require some renaming) but I hope it brings the point across.

tracer:
  open_telemetry_collector:
    grpc:
      - collector:
          url: ""
          tags: {}
      - collector:
          url: ""
          tags: {}
    http:
      - collector:
          url: ""
          tags: {}
      - collector:
          url: ""
          tags: {}

I'd be up for seeing if I could implement this if there aren't any major concerns. Any feedback would be appreciated!

[Jeffail]

Hey @DaniTulp, sounds useful so happy to add this.

[disintegrator]

@Jeffail Should we close this issue now that #1351 is merged?