For all google-cloud-* libraries that require python >=3.6, expand google-api-core, google-cloud-core and google-auth pins to >1.x.x, <3.0.0dev.

Leave a comment in the setup.py for these libraries asking library maintainers to not require >=2.x.x versions until #10566 has been closed.

Release google-cloud-* libraries with expanded pins.

dependencies = [
    # NOTE: Maintainers, please do not require google-api-core>=2.x.x
    # Until this issue is resolved:  https://github.com/googleapis/google-cloud-python/issues/10566
    "google-api-core[grpc] >= 1.26.0, <3.0.0dev",
    "proto-plus >= 1.15.0",
    "packaging >= 14.3",
]

This issue can be closed when all google-cloud-* libraries have latest releases with <3.0.0dev pins.