`fcli * action`: `check` instruction improvements

[rsenden]

To make the check instruction more versatile, we may want to consider some of the potential improvements listed below.

• Add fail/passLevel or similar attributes to check: element:
  • Identify whether a failure should be treated as informational, warning or failure
  • Identify whether success should be treated as informational or warning
  • For example, an informational/warning failure would still result in 0 exit code
  • What should we name this attribute exactly, and how should this be presented in the output?
• Add global checks configuration, defining:
  • Output location (default stdout)
  • Exit codes (default 0 for success, for failure: 1, 100, ...?)
  • What output to write (passed checks, failed checks and/or overall status)
• Custom exit codes:
  • Per check (but how to combine?)
  • In global checks configuration (see above)
  • Ability to increase based on number of failed checks or similar?