Allow deleting google_logging_*_bucket_config

[modular-magician]

Allows deleting log bucket configuration (fixes hashicorp/terraform-provider-google#11412 since I have the same use case as tracked by that issue).

The upstream API already returns a 403: Bucket _Default cannot be deleted (for undeletable buckets) but I opted not to use it because deleting _Default or _Required would always fail then.

I'm not sure whether or not there are e2e tests involved in resource deletion so I had to test them semi-manually (override provider to local built and then creating and destroying resources).

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logging: made `google_logging_*_bucket_config` deletable

Derived from GoogleCloudPlatform/magic-modules#5949