feat: Make DockerComposeConfigurator compatible with "false" string

[jawira]

This fixes #1060

With this MR DockerComposeConfigurator will recognize "false" string a proper boolean.

I use filter_var function, I think this is a good solution because it requires only a single method call to fix the issue.

With filter_var function:

• true, 1, "true", "yes", "1", and "on" are recognized as true as well.
• any other value is false.

Additionally this function is already used in the same method some lines below:

flex/src/Configurator/DockerComposeConfigurator.php

Lines 115 to 117 in 423c36e

	$answer = self::askDockerSupport($io, $recipe);
	} elseif (filter_var($_SERVER['SYMFONY_DOCKER'], \FILTER_VALIDATE_BOOLEAN)) {
	$answer = 'p';

[fabpot]

Thank you @jawira.