Add E2E tests

[joeriddles]

• https://forum.obsidian.md/t/standard-approach-for-writing-automated-end-to-end-tests-for-plugins/31535
• https://playwright.dev/docs/api/class-electron

[joeriddles]

https://forum.obsidian.md/t/e2e-testing-of-plugins-with-webdriverio/107493