[ML] ML Embeddables cause the dashboard to think there are unsaved changes

[jgowdyelastic]

If you add a swim lane or anomaly chart to a dashboard, the dashboard cannot get itself into the state where it thinks all changes have been saved. When pressing the Save button at the top right of the page, the button always returns to being active rather than disabled. Clicking the Switch to view mode button triggers a prompt that there are unsaved changes.

Other embeddables behave as expected, when pressing theSave button, it becomes disabled to signify that all changes have been saved.

To reproduce:

• create a new dashboard
• add any visualization (can be ML or any other)
• save dashboard
• add an ML visualizaton, so now the dashboard contains two visualizations.
• save the dashboard, you should now see the issue as explained above.

[elasticmachine]

Pinging @elastic/ml-ui (:ml)