[RFC] Poc config yaml

[marcalff]

Fixes #2481

Request For Comments (Proof of concept code for now)

Start with examples/yaml/main.cc

Features implemented:

• https://github.com/open-telemetry/opentelemetry-configuration
  • Full support for propagators
  • Full support for traces, including recursive sampler definitions.
• Extension points
  • Custom propagators
  • Custom samplers
  • Custom span processors
  • Custom span exporters

Changes

Please provide a brief description of the changes here.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[netlify]

✅ Deploy Preview for opentelemetry-cpp-api-docs canceled.

Name	Link
🔨 Latest commit	8420c89
🔍 Latest deploy log	https://app.netlify.com/sites/opentelemetry-cpp-api-docs/deploys/67620f8087505f0008406852