Add environment variables for global flags

[jrschumacher]

Feedback from users regarding use of CLI

Supporting env + global flags + profiles and allowing the blending of all of them creates too much burden on the team to reliably test all permutations. We would like to strictly enforce supporting only specified set of triggers.

So...

• read global flags
  • if user does not meet required flag shape then return error, DO NOT fill in with env or profiles
• read env next
  • with using env we will require a flag --use-env
  • when this flag is specified, we will ONLY use the environment variables and return an error if shape isn't met
  • we will only support client credentials
• default to profiles
  • will still defer Linux support for now
  • if on Linux, will require global flags or env

Acceptance Criteria

• follow rules above
• use the following env vars
  • {APP_NAME}_HOST
  • {APP_NAME}_TLS_NO_VERIFY
  • {APP_NAME}_CLIENT_CREDS
  • {APP_NAME}_CLIENT_CREDS_FILE