docs: add browser version support and Chrome version availability

[MikeMcC399]

• Closes Installing older versions of Chrome fail due to Google stopping support #1431

Situation

• Google Chrome purges older browser versions, so they are no longer available for building into a Cypress Docker image

• Cypress officially supports the latest 3 major versions of Chrome, Firefox, and Edge only - see https://docs.cypress.io/app/references/launching-browsers#Browser-versions-supported

This information is missing from the factory README.

Change

• Add the information that Cypress officially supports the latest 3 major versions of Chrome, Firefox, and Edge only to
  • the factory README by referring to Cypress System requirement for details of currently supported environments, including Node.js and Browsers support.
  • the factory/.env and note the availability of earlier Google Chrome versions.

[cypress-app-bot]

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