[extension/encoding] support skywalkingencoding extension

[JaredTan95]

Description

The kafkareceiver supports jaeger and zipkin protocol traces, and can also receive skywalkng traces via skywalkingreceiver.

From the practical use of skywalking, we often use kafka to host large-scale traces data. However, kafka receiver does not support skywalking encoding currently.

with this PR, we can fectch skywalking traces and parse it into otlp traces:

receivers:
  otlp:
    protocols:
      grpc:
        endpoint: 0.0.0.0:4317
  kafka:
    encoding: skywalking_encoding
    topic: skywalking-segments
    brokers:
      - "localhost:9092"
    resolve_canonical_bootstrap_servers_only: true
    client_id: otel-collector
    group_id: otel-collector
    metadata:
      retry:
        max: 10
        backoff: 5s

exporters:
  debug:

processors:
  batch:

extensions:
  health_check:
  pprof:
    endpoint: :1888
  zpages:
    endpoint: :55679
  skywalking_encoding:
    protocol: skywalking_proto

service:
  extensions: [pprof, zpages, skywalking_encoding, health_check]
  pipelines:
    traces:
      receivers: [kafka]
      processors: [batch]
      exporters: [debug]

Link to tracking issue

Fixes #28693

Testing

Documentation

[atoulme]

Please do this in a separate pr