Move gcssink config override out of the adapter

[fpacifici]

All steps that allow for the settings to be overridden provide
an override_config method.

It seems the GCSSink did not use this mechanism to override the
config.
Fixed to make it comply with the other steps

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[github-actions]

Semver Impact of This PR

⚪ None (no version bump detected)

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• Move gcssink config override out of the adapter by fpacifici in #228

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