[kitcli] Make uploading config to S3 more robust

Ref: https://github.com/awslabs/kubernetes-iteration-toolkit/pull/113#discussion_r785214318

Start with the linked PR 113 discussion and trace the kitcli code that uploads configuration to S3. Identify the specific robustness concern described there, then inspect the repository’s existing checks for that upload path; done means the discussed concern is resolved and those checks pass.

Written by the indexing model from the issue text.