Release 1.59.0

Context

• Clarify that environment variable propagation operational guidance is
  non-normative and should be documented by language implementations.
  (#5165)
• Clean up implementation guidelines for environment variable propagation
  carriers.
  (#5166)
• Remove caching behavior suggestions for environment variable propagation
  carrier implementations.
  (#5179)
• Mark "Environment Variables as Context Propagation Carriers" as Release
  Candidate.
  (#5142)

Traces

• Amend the description of Composite/Composable samplers.
  (#5161)

Logs

• Add ETW (Event Tracing for Windows) example mapping to the logs data
  model appendix, including the ETW level to SeverityNumber mapping.
  (#5159)

Profiles

• Add Profiles data model (data-model.md).
  (#4965)

Supplementary Guidelines

• Add non-normative supplementary guidelines for SDK self-observability.
  (#5135)

OTEPs

• Add OTEP proposing a central OpenTelemetry benchmarks repository.
  (#5118)
• Introduce Policies into the specification.
  (#4738)

New Contributors

• @swashtek made their first contribution in #5159
• @oindrilakha12-ui made their first contribution in #5194