Show last activity in submission summary panel

[NateWr]

Describe the problem you would like to solve
Editors want to be able to see recent editorial activity on a submission without loading the submission workflow page.

Describe the solution you'd like
Add the most recent activity and a button to open the activity log to the submission summary panel.

Who is asking for this feature?
This came out of user testing for #7495.

Additional information
This issue depends on the summary panel in #8883.

Here is a mockup showing what the last activity could look like.

And the button could open a modal with the activity log or a secondary side panel like this.