Set up e2e testing

[marcus-crane]

Now that I have a proper Microsoft 365 Developer account set up, I can actually test this plugin locally.

Prior to now, I didn't actually have access to try out different settings.

As a result, it should be possible to set up a pipeline dedicated to running e2e login using the plugin.

With this, we can identify regressions and that errors are surfaced where expected.

[marcus-crane]

Having annoying issues with the Testcafe Docker image, probably because it's headless and something something. Might try out Cypress since it's generally the recommended tool. I only erred initially on using it as (in the past anyway), it was big on only having a single domain that you don't navigate away from. Moving to the MS login page and back violates that condition but it might be more lenient nowadays.