This commit refactors the GCS storage driver from the ground up and makes
it more consistent with the rest of the storage drivers.
We are also fixing GCS authentication using default app credentials:
When the default application credentials are used we don't initialize the
GCS storage client which then panics.
Co-authored-by: Cory Snider <corhere@gmail.com>
Signed-off-by: Milos Gajdos <milosthegajdos@gmail.com>
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