Migrate cloudtrace propagator to contrib

[brettmc]

Per https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/context/api-propagators.md#propagators-distribution vendor-specific propagators must not be maintained in the core repo.

• [x] merge and publish https://github.com/open-telemetry/opentelemetry-php-contrib/pull/418
• [ ] abandon https://packagist.org/packages/open-telemetry/extension-propagator-cloudtrace (suggest contrib version as the replacement)
• [ ] merge #1678

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[weslenteche]

Hi @brettmc I can take this up.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.