[SPIKE 5 days] Investigate cross browser testing

[rmccar]

Currently we do not have cross browser testing in place. This is leaving us open to browser specific bugs that we may never know are an issue. We only test on chrome through puppeteer in our visual regression tests. We used to test on multiple browsers using Browserstack and Percy. This was replaced with BackstopJS because of costs.

We should investigate if there is a way of using BackstopJS to test in multiple browsers. Or if not there are any free alternatives that we could use to do this.

We will need to take into consideration the length of time these tests will take to run and when they should be run. Currently we run BackstopJS on every PR and just using Chrome that is taking around 45 mins to run our tests which is already very long. How much longer will it take if we start testing in multiple browsers?

Spike outcomes
List of options and associated costs
Present back to team MVP