Contribute resource detector to opentelemetry-python-contrib

[aabmass]

Similar to GoogleCloudPlatform/opentelemetry-operations-js#518 and what we did for Go and Java. We should contribute either the detector class with it's minimal logic, or just "re-export" the detector class in a new package in opentelemetry-python-contrib

opentelemetry-operations-python/opentelemetry-resourcedetector-gcp/src/opentelemetry/resourcedetector/gcp_resource_detector/_detector.py

Line 31 in 73b6ac1

class GoogleCloudResourceDetector(ResourceDetector):

The implementation logic should stay in this repo since we run integration tests against it.