Otel config (#782)

* General restructring of Otel configuration

```yaml
telemetry:
  apollo:
    endpoint:
    apollo_graph_ref:
    apollo_key:
  tracing:
    propagation:
      # Propagation is automatically enabled for any exporters that are enabled
      # but you can enable extras. This is mostly to support otlp.
      zipkin: true
      datadog: false
      trace_context: false
      jaeger: false
      baggage: false

    otlp:
      endpoint: Default
      protocol: Grpc
      http:
        ..
      grpc:
        ..
    zipkin:
      agent:
        endpoint: Default
    jaeger:
      agent:
        endpoint: Default
    datadog:
      endpoint: Default

    # Trace config is shared across all exporters
    trace_config:
      # Env variables can be used anywhere in any plugin config
      service_name: "${ENV_VARIABLE}"
  metrics:
    ..

```

Each of the exporters has its own source file.

Other notes:
* Otel provides integration with http for propagation. Removed our custom code and use the library.
* Remove our propagation layer, otel provides propagators for each exporter.
* Fix header extraction. Spans can now be collated from client to subgraphs.
* Update supgergraph demo so that span propagation takes place
* Unfied metrics and tracing config
* Config enums changes to snake_case 

There is an issue round sampling that needs to be followed up on.
Sampling happens at the pipeline level, so if the user enables sampling then discarded samples will not make it to spaceport. We need to discuss what we are going to do about this.

Co-authored-by: bryn <bryn@apollographql.com>
Co-authored-by: Geoffroy Couprie <geoffroy@apollographql.com>
Co-authored-by: Coenen Benjamin <benjamin.coenen@hotmail.com>

.circleci/config.yml

@@ -242,10 +242,7 @@ commands:
     steps:
       - rust/build:
           with_cache: false
-          crate: --locked --features otlp-grpc -p apollo-router -p apollo-router-core
-      - rust/build:
-          with_cache: false
-          crate: --locked --no-default-features --features otlp-http -p apollo-router -p apollo-router-core
+          crate: --locked -p apollo-router -p apollo-router-core
   build_all_permutations:
     steps:
       - build_common_permutations