@grafana/plugin-e2e API tests

The purpose of the E2E tests in this directory is not to test the plugins per se - it's to verify that the fixtures, models and expect matchers provided by the @grafana/plugin-e2e package are compatible with the latest version of Grafana. If you find that any of these tests are failing, it's likely because you have made changes in the Grafana UI that breaks the end-to-end testing APIs in plugin-e2e. For information on how to address this, follow the instructions in the contributing guidelines for the @grafana/plugin-e2e package in the plugin-tools repository.