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.

• merge and publish migrate extension propagator cloudtrace opentelemetry-php-contrib#418
• abandon https://packagist.org/packages/open-telemetry/extension-propagator-cloudtrace (suggest contrib version as the replacement)
• merge migrate/remove cloudtrace propagator #1678

[stale]

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[weslenteche]

Hi @brettmc I can take this up.

[stale]

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.