feat: support W3C propagation headers

[dmehala]

Description

• Enable OTLP Ingestion on Pongo's agent container.
• Add W3C injection/extraction propagation headers.
• Add configurable propagation styles. For now, only datadog and tracecontext are supported.
• Revise README.md to include updated configurations for propagation.
• Add new unit tests for W3C propagation headers.

How to test

_format_version: "3.0"
_transform: true

services:
- name: service-a
  url: http://localhost:8000/bar
  plugins:
  - name: ddtrace
    config:
      service_name: service-a
      agent_host: datadog-agent
  routes:
  - name: my-route-a
    paths:
    - /foo

- name: service-b
  url: http://httpbin.org/headers
  plugins:
  - name: opentelemetry
    config:
      endpoint: http://datadog-agent:4318/v1/traces
      resource_attributes:
        service.name: service-b
  routes:
  - name: my-route-b
    paths:
    - /bar

Run: curl -i http://localhost:8000/foo

Result:

TODO:

• [ ] Self code review
• [ ] README.md

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