Excerpt Suggestions: Allow different personas/styles

[acicovic]

Is your feature request related to a problem?

In Excerpt Suggestions, we currently don't offer a way to customize the persona and style. We recently received internal feedback that this would be desirable, since the current persona/style isn't ideal for writings of certain types (e.g. documentation).

Describe the solution you'd like

Provide controls to specify persona and style, as we currently do in our Title Suggestions feature.