[CLI] Automatically create customization files for detected changes

[peterjuras]

Summary

coat sync prompts when a file that is managed by coat has been modified and overwrites the current file with the generated contents.

In certain situations, coat could detect what has been modified and offer to automatically create a customization file that achieves the same outcome.

Example:

Given the following generated coat file:

// config.json
{
  "config": "value"
}

And the following modified disk content:

// config.json
{
  "config": "value",
  "custom": "custom-value"
}

coat could offer to create a customization file that will result in the modified file:

// config.json-custom.js
module.exports = {
  custom: "custom-value",
};