[Stack Monitoring] Alert editing fly-out shows outdated alert parameters after editing

[weltenwort]

Kibana version: 7.12.0-BC4

Elasticsearch version: 7.12.0-BC4

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

Describe the bug: After editing an alert via the fly-out from the stack monitoring UI, opening the same alert editing flyout again shows the values before the last edit.

Steps to reproduce:

1. Navigate to stack monitoring
2. Ensure the built-in alerts are present
3. Make a change to one of the alerts via the fly-out and save the change (such as changing the message)
4. Open the editing fly-out for the same alert again immediately afterwards
5. Observe, that the values don't reflect the last edit

Expected behavior: The fly-out is populated with up-to-date alert configuration parameters when it's being opened.

[elasticmachine]

Pinging @elastic/stack-monitoring (Team:Monitoring)