[ale18V]

Cypress is officially planning to deprecate its bundled Electron test browser:

• Cypress Launching Browsers Documentation
• Migrating Away from Electron
• Cypress GH Action Browser

In addition, Electron exhibits subtle behavioral and rendering divergences in headless Linux environments (e.g. forced --disable-gpu and software fallback quirks).

This PR:

1. Updates the GitHub Actions CI workflows to explicitly execute Cypress test jobs in Google Chrome (browser: chrome).
2. Adds support for selecting the Cypress browser via the DISCO_E2E_BROWSER environment variable (e.g. DISCO_E2E_BROWSER=firefox, chrome, edge).
3. Documents browser selection for E2E tests in docs/CONTRIBUTING.md.

[ale18V]

As a side note: the cypress action GH action documentation states that the defaultBrowser of the cypress config is used if none is specified in the action parameters. And if that is undefined then electron is used (which is the case RN).

@JulienVig two points:

1. I didn't set an explicit fallback in the defaultBrowser - it's only set by the env variable right now. I didn't want to hardcode chrome or firefox as it depends on which browser the developer is used to on their system. Do we want to have a default browser such as chrome same for everyone when the env var is not set?
2. Even if we set the defaultBrowser I think it's better to be explicit and still set the browser in the action params which is what this PR does.

[JulienVig]

All good thanks! Being explicit on the CI browser sounds fine to me. However I think we should set a fallback browser.