[ML][UX]: Updates to ML embeddable 'Add to' action

[mdefazio]

Follow up from https://github.com/elastic/kibana/pull/183423

The overflow button currently (8.14) in the Single Metric Viewer is hard to notice and feels out of place with the alignment of the visualization.

Some proposals for improving the visibility of this action:

• Add all actions to a single row: checkboxes, Add to and Forecast.
• Change overflow button to EuiButton rather than EuiButtonEmpty with color 'text'.
• Recommend putting this at the end of the row, as it's an 'overflow' button. But if we want Forecast to be the last action, then I'd recommend changing the icon to share or export or simply giving this button the label 'Add to' with the a down arrow on the right.

The following screenshots show these two options:

Option 1

Option 2

As part of this, can we update the toast action that follows:

Include the default button in the toast. Optionally update the copy so it's mentioned that the visualization was added to the case. (Particularly when creating a new case, it's not immediately clear that the case was created and this was added to it.

[elasticmachine]

Pinging @elastic/ml-ui (:ml)

[peteharverson]

Note that we also use the same UX for adding to dashboard / case from the Anomaly Explorer and the ML AIOps Labs Change Point Detection views, so we should extend any changes to those two views too.