v7 release: Alpha release of core packages:

• opentelemetry-api
• opentelemetry-sdk

and exporter packages:

• opentelemetry-exporter-otlp
• opentelemetry-exporter-etw
• opentelemetry-exporter-zipkin
• opentelemetry-exporter-jaeger

Changelog:

• [METRICS] Move metrics api/sdk under preview feature flag (#745)
• [DOCS] Add instructions to build using Bazel (#747)
• [DOCS] Update copyright headers (#754)
• [EXPORTER] Populate resource to OTLP proto data (#758)
• [CI] Add CodeQL security scan CI workflow (#770)
• [BUILD] Enable building API only CMake Project (#778)
• [SDK] Fix for sampling of root span (#784)
• [CI] Add Jaeger exporter to CMake CI build (#786)
• [API] BREAKING CHANGE - Tracer::WithActiveSpan() to return Scope object intead of unique_ptr (#788)
• [DOCS] Add docs for nested spans and context propagation in readthedocs (#792)
• [CI] Output verbose error for failed unit-test in CI (#796)