NIFI-3514 - Ensures ListGCPBucket triggers serially and forbids inputs

[trixpan]

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[trixpan]

@jvwing @gene-telligent - would you mind having a look ?

[jvwing]

@trixpan - Good catch. I had asked @gene-telligent to remove INPUT_ALLOWED, but explicitly declaring INPUT_FORBIDDEN is a best practice. I will review.

[jvwing]

@trixpan Thanks again for those annotation changes. I agree they are necessary for the stability and consistent usage of ListGCSBucket.