CloudFormationManagedUploadInfrastructure setup issues

A customer attempted to register modules using CodeBuild and reported this to us:

- The registration failed with "internal failure". It was not clear what the error was. In the end it turned out that the CodeBuild service role was missing `kms:decrypt` permissions against the KMS key used by the S3 bucket (the same KMS Key generated by the CloudFormationManagedUploadInfrastructure stack). CFN CLI should give more descriptive error messages.
- When `CloudFormationManagedUploadInfrastructure` generates, the stack should provide a "AWS::KMS::Alias" to simplify KMS key management, KMS permissions, and with making templates across many accounts.
- We should provide guidance on what the `CloudFormationManagedUploadInfrastructure` stack is and what it does. (For this point, i'm not sure if this should be explained in this repo, or in the CloudFormation user guide).

Inizia tracciando il flusso di registrazione di CFN CLI e lo stack CloudFormationManagedUploadInfrastructure menzionato nel report. Verifica come vengono esposti gli errori interni e come viene generata la chiave KMS, quindi esamina la domanda nella guida utente di CloudFormation. Il lavoro sarà considerato completato quando le indicazioni sugli errori richieste, l'alias KMS e la spiegazione dello stack avranno responsabili chiari e modifiche corrispondenti all'implementazione o alla documentazione.

Scritto dal modello di indicizzazione a partire dal testo della issue.