OPENEUROPA-373: Implements command hooks

[ademarco]

We could easily provide pre and post command hooks based on naming conventions, just like what we currently do for drupal:site-install.

It would look like this:

Given I have a "my-custom:command"
And I add dynamic pre/post hooks as:
"""
hooks:
    my-custom:command:
        pre:
          - { task: "symlink", from: "../../../../..", to: "${drupal.root}/sites/all/themes/custom/ec_europa" }
          - { task: "run", command: "drupal:drush-setup" }
          - { task: "run", command: "drupal:settings-setup" }
        post:
          - "./vendor/bin/drush --root=$(pwd)/${drupal.root} cr"
"""
Then pre and post hooks are ran automatically before and after "my-custom:command"
And I can run the following commands via the command line:
"""
$ hooks:pre:my-custom:command
$ hooks:post:my-custom:command
"""

This should also work for non-custom commands.

[ademarco]

Closing as this is now tracked by OPENEUROPA-373.