Allow configuration via command-line options

[ikretz]

This PR adds command-line options to the scfw configure subcommand so that users may configure the command non-interactively via scripting.

usage: scfw configure [-h] [--alias-pip] [--alias-npm] [--dd-api-key KEY] [--dd-log-level LEVEL]

Configure the environment for using Supply-Chain Firewall.

options:
  -h, --help            show this help message and exit
  --alias-pip           Add shell aliases to always run pip commands through Supply-Chain Firewall
  --alias-npm           Add shell aliases to always run npm commands through Supply-Chain Firewall
  --dd-api-key KEY      API key to use when forwarding logs to Datadog
  --dd-log-level LEVEL  Desired logging level for Datadog log forwarding (options: ALLOW, ABORT, BLOCK)

If no command-line options are present, the interactive script runs as it did previously. Otherwise, the command-line configuration is used and no output is printed.

The PR also performs various small refactoring.

[sobregosodd]

LGTM