Implement E2E tests at the branch/PR level

[rwood-moz]

Currently the Appointment E2E production sanity test suite runs nightly as well as after every production deployment, on the Appointment production environment via GHA and BrowserStack. It is a good safety net to find production issues that may slip through. Now update the test framework so that E2E tests will also run at the branch / PR level so that any potential issues will be caught within PRs and before production releases. At first the E2E tests ran at the PR level will be the same tests currently running as part of the production sanity test; however in the future more E2E tests will be added at the PR level to expand into more user flows (but that will be covered in a different future issue not this one).