fix: skip writing RequestLogEntry for Cloud Run with flag enabled

[cindy-peng]

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Fixes #795 🦕

This is a fix similar to the fix in nodejs-logging-bunyan to skip writting parent request log entries for cloud run.

To avoid breaking changes on the existing applications on Cloud Run, we introduce a optional parameter "skipParentEntryForCloudRun" to control the behavior. Right now the default behavior is still to create an request log entry unless "skipParentEntryForCloudRun" is set to be true specifically. We can change the default behavior in the next major release.

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