Adding handling for inner single quotes within shell_transforms

[JacobBas-Coalitioninc]

Hi, thanks for all of the work that you've put into this project!

When attempting to run a shell_transform with a python script I have a complex json string that includes inner single quotes that are not escaped out of.

For example, if I have the following json request:

{"flag_exists": "it doesn't"}

I'm met with the following error when running on a UNIX machine:

Error: Command failed: python3 /path/to/script.py '{"flag_exists": "it doesn't"}' 'other'

This is even shown in the code highlighting above. It looks like the tests are already sort of aware of this: https://github.com/bbyars/mountebank/blob/master/test/models/behaviors/shellTransformTest.js#L47-L52

I believe that the place that this needs to be fixed is given below where if you add something along the lines of the below chunk it would fix the issue:

`'${json.replace(/'/g, '\'')}'`; 

https://stackoverflow.com/questions/1250079/how-to-escape-single-quotes-within-single-quoted-strings#:~:text=I%20can%20confirm%20that%20using,quotes%20here%20are%20single%20quotes).

mountebank/src/models/behaviors.js

Lines 141 to 153 in 005aac0

	function quoteForShell (obj) {
	const json = JSON.stringify(obj),
	isWindows = require('os').platform().indexOf('win') === 0;
	if (isWindows) {
	// Confused? Me too. All other approaches I tried were spectacular failures
	// in both 1) keeping the JSON as a single CLI arg, and 2) maintaining the inner quotes
	return `"${json.replace(/"/g, '\\"')}"`;
	}
	else {
	return `'${json}'`;
	}
	}

[symonk]

same problem on unix; data inclusive of single quoted strings aren't correctly escaped for the shell resulting in something along the lines of: {"foo": "'<bar>'"} trying to redirect to a file breaking the shell transform delegation to a python script for example