[CONFIG] Implement file configuration

[marcalff]

The spec for file configuration is shaping up, opentelemetry-cpp needs to start planning for this.

• https://github.com/open-telemetry/oteps/pull/225
• https://github.com/open-telemetry/opentelemetry-specification/pull/3805
• https://github.com/open-telemetry/opentelemetry-specification/pull/3840
• https://github.com/open-telemetry/opentelemetry-specification/pull/3850
• https://github.com/open-telemetry/opentelemetry-specification/pull/3948
• https://github.com/open-telemetry/opentelemetry-specification/pull/3804
• https://github.com/open-telemetry/opentelemetry-specification/pull/3802
• https://github.com/open-telemetry/opentelemetry-specification/issues/3752
• https://github.com/open-telemetry/opentelemetry-specification/issues/3967
• https://github.com/open-telemetry/opentelemetry-specification/issues/3966
• https://github.com/open-telemetry/opentelemetry-configuration/issues/100

Spec: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/configuration/file-configuration.md

Sub tasks:

• [X] Define the config file format (yaml)
• [X] Define the config file schema - experimental, see https://github.com/open-telemetry/opentelemetry-configuration
• [ ] Pick a yaml parser
  • [X] Evaluate yaml-cpp - DO NOT USE
  • [X] Evaluate libyaml - DO NOT USE
  • [X] Evaluate rapidyaml - OK technically. MIT License.
  • [ ] Legal - confirm license compatibility, see https://github.com/open-telemetry/community/issues/2383
  • [ ] Evaluate other choices.
• [X] Define C++ classes for the config model
  • [X] Propagators.
  • [X] Traces.
  • [X] Metrics.
  • [X] Logs.
• [X] Implement environment variables substitution from yaml
• [X] Populate the C++ config model from yaml
  • [X] Propagators.
  • [X] Traces.
  • [X] Metrics.
  • [X] Logs.
• [ ] Instantiate SDK and exporter objects from the C++ config model
  • [X] Propagators.
  • [X] Traces.
  • [ ] Metrics.
  • [ ] Logs.
• [ ] User documentation
• [X] Define a registry for plugin components
  • [X] propagators
  • [X] trace plugins
    • [X] samplers
    • [X] span processors
    • [X] span exporters
  • [ ] metric plugins
  • [ ] logs plugins
• [X] Populate config model from yaml, for registered third party components
  • [X] propagators
  • [X] trace plugins
    • [X] samplers
    • [X] span processors
    • [X] span exporters
  • [ ] metric plugins
  • [ ] logs plugins
• [X] Instantiate plugins from config model, for registered third party components
  • [X] propagators
  • [X] trace plugins
    • [X] samplers
    • [X] span processors
    • [X] span exporters
  • [ ] metric plugins
  • [ ] logs plugins
• [ ] Third party documentation (for implementing plugins)

Related issues, found while implementing this feature:

• community
  • https://github.com/open-telemetry/community/issues/2383
• opentelemetry-configuration
  • https://github.com/open-telemetry/opentelemetry-configuration/issues/70
  • https://github.com/open-telemetry/opentelemetry-configuration/issues/72
  • https://github.com/open-telemetry/opentelemetry-configuration/issues/74
  • https://github.com/open-telemetry/opentelemetry-configuration/issues/75
  • https://github.com/open-telemetry/opentelemetry-configuration/issues/108
  • https://github.com/open-telemetry/opentelemetry-configuration/issues/109
• opentelemetry-specifications
  • https://github.com/open-telemetry/opentelemetry-specification/issues/3894
  • https://github.com/open-telemetry/opentelemetry-specification/pull/3913
  • https://github.com/open-telemetry/opentelemetry-specification/issues/3920
• opentelemetry-cpp
  • https://github.com/open-telemetry/opentelemetry-cpp/issues/2545
  • https://github.com/open-telemetry/opentelemetry-cpp/issues/2552
  • https://github.com/open-telemetry/opentelemetry-cpp/issues/2664
• ryml
  • https://github.com/biojppm/rapidyaml/issues/455
  • https://github.com/biojppm/rapidyaml/issues/458
  • https://github.com/biojppm/rapidyaml/issues/468