[SECRES-3850] Handle non-interactive shells gracefully

[ikretz]

This PR adds a check during scfw run for whether we're running in a non-interactive shell. This is relevant when the user must provide interactive input to confirm a command with only warning-level findings. Instead of erroring out, SCFW now defaults to blocking in this situation. Users can change this default behavior by adding --allow-on-warning to their SCFW command-line.

For cases where users are unable or unwilling to update their command lines, this PR also allows users to configure this auto-allow/auto-block behavior by setting a new environment variable SCFW_ON_WARNING to "ALLOW" or "BLOCK".

The command-line options and environment variables determine the warning-level action as follows:

1. If --block-on-warning or --allow-on-warning is set, behave accordingly
2. Else if SCFW_ON_WARNING is set and valid, behave accordingly
3. Else if in a non-interactive shell, BLOCK,
4. Else, ask the user for confirmation and act accordingly

Other changes include:

• Adding more precise error checking and logs while configuring the Datadog Agent
• Update README with detail on useful CLI options and the new environment variables
• Move the file containing configuration-related constants to the top-level directory