Change the task compiler logic to allow resolving of environment variables.

[veewee]

Q	A
Branch	master
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
Documented?	no
Fixed tickets	#1146

Fixes #1146

This allows for task configurations to resolve environment variables.
Example:

grumphp:
    tasks:
        phpunit:
          testsuite: "%env(string:PHPUNIT_TESTSUITE)%"
          metadata:
            enabled: '%env(bool:PHPUNIT_ENABLED)%'

PHPUNIT_TESTSUITE=Foo PHPUNIT_ENABLED=1 ./bin/grumphp run

or, you can make it work with environment configurations:

grumphp:
  environment:
    variables:
      PHPUNIT_ENABLED: "1"
      PHPUNIT_TESTSUITE: "Foo"

[veewee]

@kira0269, Thanks for your comments;

In this PR, I focused on getting the environment variables working inside the task configurations.
I agree that some parts during bootstrapping Grumphp or configuring the tasks could be improved.
Since it works right now and I don't want to reinvent the wheel with no real gain, I'm not sure it's worth the time or trouble to work on this.

Anyways, thanks for your feedback and for figuring out how to solve the issue :)

[oallain]

Thanks for that @veewee 🎉