Introduce --about command for printing Open Source attributions

[JackuB]

Ever since Snyk CLI started bundling its npm packages, we generated an attributions file that was part of the npm package we distributed.

However, since we also distribute single executables, we should expose the attribution information from the CLI interface itself. This PR introduces an --about option, with a same importance as --version. This option will print out the license information if libraries bundled into the Snyk CLI. I chose about as a command name following an SO thread.

Since thirdPartyNotice.json is now a runtime dependency, this PR also moves the file generation step to the main webpack config file.

[github-actions]

	Warnings
⚠️	Since the CLI is unifying on a standard and improved tooling, we're starting to migrate old-style imports and exports to ES6 ones. A file you've modified is using either module.exports or require(). If you can, please update them to ES6 import syntax and export syntax. Files found: src/cli/args.ts webpack.common.ts

	Messages
📖	You are modifying something in test/smoke directory, yet you are not on the branch starting with smoke/. You can prefix your branch with smoke/ and Smoke tests will trigger for this PR.

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