Add pyodide BrowserStack tests

[loiswells97]

• BrowserStack can be integrated into our existing workflow using Github Actions. BrowserStack have their own actions that we can use to automate the setup and running of BrowserStack tests.
• There is a jest library backed up by selenium that could be used to write automated BrowserStack tests. More investigation is needed to determine the exact syntax required.
• A browserstack.yml file is used to specify the configuration for the tests, for example, which devices, operating systems and browsers to run the tests in - it might be useful for us to think through which setups we want to prioritise testing on.
• We could prioritise testing the final projects for a couple of the projects on the python paths, for example:
  • hello-world-solution would enable us to test whether pyodide correctly handles input and the stop button
  • charting-champions-example would allow us to test the use of pygal (e.g. does the program run without error?) and external data files

[sra405]

@grega this might be of use