Kibana version: 7.8.0-BC1

Original install method: cloud

Describe the bug: Attempting to create a connector for either the "index", "pager duty" or "slack" alert action connector in-line within the alert creation fly-out causes the UI to break with the exception shown below.

Steps to reproduce:

1. Navigate to the metrics explorer in the Kibana metrics UI.
2. Click the "Create alert" link in the "Alerts" popover.
3. Choose the "Slack" action type.
4. Click "Create a connector".
5. Observe the exception.

Expected behavior: The appropriate connector creation form is shown.

Screenshots:

Errors in browser console: