Support arbitrary paths for plugins

[lucatume]

Allow the WPLoader module plugins and silentlyActivatePlugins parameters to point to arbitrary plugin paths.

The paths can be absolute paths like /home/projects/my-plugin/plugin.php, paths relative to the project root directory like vendor/woocommerce/woocommerce.php, directory/file.php or file.php paths relative to the WordPress installation plugins directory.

E.g. this configuration will work:

actor: IntegrationTester
bootstrap: _bootstrap.php
modules:
  enabled:
    - \Helper\Integration
    - lucatume\WPBrowser\Module\WPLoader:
        wpRootFolder: /var/wordpress
        dbUrl: mysql://root:root@mysql:3306/wordpress
        tablePrefix: test_
        domain: wordpress.test
        adminEmail: admin@wordpress.test
        title: 'Integration Tests'
        plugins:
          - hello.php # This plugin will be loaded from the WordPress installation plugins directory.
          - /home/plugins/woocommerce/woocommerce.php # This plugin will be loaded from an arbitrary absolute path.
          - vendor/acme/project/plugin.php # This plugin will be loaded from an arbitrary relative path inside the project root folder.
          - my-plugin.php # This plugin will be loaded from the project root folder.
        theme: twentytwentythree