refactor: convert command-helpers and aws-util modules to yargs

[rossiam]

• converted command-helpers module to yargs
• converted aws-util module to yargs
• fixed bug with inquirer erroring out when we give it an undefined value for its validate function
  • updated inquirer to latest version 9 (this didn't help but I left it in)
  • ensure we completely leave out validate if we don't need it
• misc. minor cleanup and formatting
• added cancelCommand function to util

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Latest commit: cfc6b9e9985585d2b4620bf18709a21fd8088858

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