[Uptime] Alert flyout is broken

[justinkambic]

Kibana version:
master

Elasticsearch version:
master

Server OS version:
macOS

Browser version:
Chrome 83.x

Browser OS version:
macOS

Original install method (e.g. download page, yum, from source, etc.):
from source

Describe the bug:
The monitor status alert flyout is crashing with an error when it should display without issues.

Steps to reproduce:

1. Open the Uptime UI
2. Click the alerts dropdown and select Monitor Status
3. Observe the error

Expected behavior:
The flyout should display controls for editing the alert.

Screenshots (if relevant):

Errors in browser console (if relevant):

Uncaught TypeError: can't access property "errors", alertType.validate(...) is undefined

Provide logs and/or server output (if relevant):

Any additional context:
This likely resulted from a recent optimization we added in #70632, which I approved. During the review I failed to notice the alert flyout wasn't working. Once we reenable the test in #72963 we should be resilient to failures like this.

[elasticmachine]

Pinging @elastic/uptime (Team:uptime)