[ML] Transforms: Improve error handling/toast bursts in transforms list

[walterra]

On the transforms list page, when doing bulk actions, each action will result in an individual toast message (either to confirm a successful action or an error message). For many actions, this can result in toast bursts.

Example:

We should improve the behaviour, for example, if all actions are successful we could show only one combined toast. For errors, the toast content can be minimized/simplified, and the full error can be more explanatory. In addition, having a shorter timeout might be good as well.

[elasticmachine]

Pinging @elastic/ml-ui (:ml)