Update DAB CLI to return appropriate exit codes based upon exit reason

[seantleonard]

Why make this change?

• Closes [Bug]: Dab start command exited with code 0 #1777
  • Certain failures that occurred within CLI execution resulted in the CLI returning exit code 0 for success, even though there were failures.
    • For example, dab start {options} may contain fully valid values, but when used as arguments to start the DAB engine process within CLI, engine startup fails. The failure didn't get reflected as error code -1.
    • For example, dab init {options} may reference a file that already exists in the path that the CLI uses to read/write config files, this results in an error that is not properly reflected in the exit code.

What is this change?

• Any failures that occur in CLI usage will result in the proper exit codes:
  • 0 success
  • -1 failure
• The change updates the usage of CommandLineParser. Instead of swallowing exceptions and the status of isSuccess within the options.Handler() methods, the handler methods all return the int error code now.
• e.g. the following now captures the return codes after command line parsing.

parser.ParseArguments<InitOptions, AddOptions, UpdateOptions, StartOptions, ValidateOptions, ExportOptions, AddTelemetryOptions>(args)
                .MapResult(

How was this tested?

• Integration Tests

[seantleonard]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 2 pipeline(s).

[Aniruddh25]

Looking for const codes to indicate success or error

[Aniruddh25]

LGTM.

[aaronburtle]

Looks good, just a nit.

[seantleonard]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 2 pipeline(s).