**What this PR does**:
Adds our first UI integration test using
[Playwright](https://playwright.dev/) and runs the test on CI. Right now
the test:
- logs into Grafana
- configures the plugin (if it isn't already)
- creates an OnCall schedule, where the current user will be OnCall
- creates an escalation chain to notify based on the newly created
OnCall schedule
- creates a webhook integration, attached to the created escalation
chain
- sends a demo alert for the new integration
- goes to the alert groups page and validates that the escalation step
to alert the OnCall user actually happened
Currently the Playwright tests are run against the 3 default headless
browsers, chromium, Firefox, and webkit. The CI job that runs these
tests is run as a matrix against 3 tagged versions of `grafana`; `main`,
`latest`, and `9.2.6`.
Secondly, it adds most of the logic for a second test which:
- logs into Grafana
- configures the plugin (if it isn't already)
- goes to the user's settings, verifies their phone number (using a tool
called [MailSlurp](https://www.mailslurp.com/))
- configures the current user's default escalation policy to send alerts
via SMS
- creates an escalation policy and configures it to send alerts to our
current user
- creates an integration and assigns the created escalation policy
- triggers a test alert + verifies that we receive the SMS alert text
(again, using MailSlurp)
**Which issue(s) this PR fixes**:
Closes#873
**Checklist**
- [x] Tests updated
- [ ] Documentation added (N/A)
- [ ] `CHANGELOG.md` updated (N/A)
