New End-to-end automated behavior tests

[JalilArfaoui]

This is mostly an «issuation» of the existing PR #289

We want to automate the - currently manual - acceptance and non-regression tests in order to

• Faster validation
• Avoid missing checks
• CLI only launch (no need to touch the browser)
• As close as possible to real world
• Shorter feedback loop : validate scenarios before merging anything
• (Later) Embedded in CI pipeline so that regression check is done all the time
• Concentrate on more explorary testing on staging
• Use BDD written feature so minimize the gap between domain experts and developers

Target user
@dis-moi/product , @dis-moi/devs and all users as end beneficiaries

Technical implementation notes
PR #289 already has 80% of the work done 😭

Use case description example

Feature: Matching context
  In order to read relevant notice
  As a user
  I want to see notices that match my current tab context

  Scenario: Open Pixmania homepage
    When I open the url "https://pixmania.fr"
    Then I see the notification within 10 seconds
      And a notice has text "Que choisir signale que de nombreux clients mécontents"