Add support in SDK's for Environment Variable Context Propagation in support of Spec Changes

[adrielp]

Overview

In order to support the recent specification changes, we want to add support for the specification in multiple library repositories so that downstream users can get the benefits of cross-process context propagation.

Repositories to Update

• https://github.com/open-telemetry/opentelemetry-go
• https://github.com/open-telemetry/opentelemetry-python
• https://github.com/open-telemetry/opentelemetry-dotnet
• https://github.com/open-telemetry/opentelemetry-js

Stretch

• https://github.com/open-telemetry/opentelemetry-ruby
• https://github.com/open-telemetry/opentelemetry-cpp
• https://github.com/open-telemetry/opentelemetry-java
• https://github.com/open-telemetry/opentelemetry-php
• https://github.com/open-telemetry/opentelemetry-swift
• https://github.com/open-telemetry/opentelemetry-erlang
• https://github.com/open-telemetry/opentelemetry-rust

Implementation Issues/Tasks

• Support the environment variable propagation spec in Python opentelemetry-python#4829