[WIP] Bootstrap end to end tests with cypress

Summary:
Setup an environment to perform end to end tests using the cypress Test Runner.

Before running the tests, Software Heritage web application is executed in the
background using in-memory storages for fetching data contained in a sample archive.

To easily run the tests, two new make targets have been added:

• test-frontend: Run tests in headless mode (this should be used in a CI environment)
• test-frontend-ui: Run tests using the cypress GUI

As an example, a couple of tests regarding the highlighting of lines of code have been added.

Related T1768

Reviewers: Reviewers

Subscribers: shisus, kalpitk

Differential Revision: https://forge.softwareheritage.org/D1565