[Draft] Setup behat testing

Created by: mbovel

This is a work-in-progress, not ready yet to review or merge.

The goal of this PR is to setup behat tests and the necessary config to run them both locally and on the CI.

It's mainly cherry-picking what we need from https://github.com/moodlehq/moodle-docker. See also https://moodledev.io/general/development/tools/behat.

moodle-assignsubmission-autograding/tests/behat/app.feature

+@javascript @app @moodledocker
+Feature: The app starts in behat
+  In order to test that the app it working properly
+  As moodle-docker
+  I need a way to verify this
+
+  Scenario: Start the app
+    Given the following "users" exist:
+      | username | firstname | lastname | email                |
+      | student1 | Student   | 1        | student1@example.com |
+    And the following "courses" exist:
+      | fullname | shortname | category |
+      | Course 1 | C1        | 0        |
+    And the following "course enrolments" exist:
+      | user     | course | role    |
+      | student1 | C1     | student |
+    And the following "activities" exist:
+      | activity | course | idnumber | name    | intro           |
+      | label    | C1     | label1   | Label 1 | It worked great |
+    When I entered the course "Course 1" as "student1" in the app
+    Then I should find "It worked great" in the app