[Task]: refactor addon_important_changes_actions in reviewers/views.py::review

[eviljeff]

Description

follow-up to mozilla/addons-server#24308

We have a hardcoded list of activity classes that should be highlighted as important changes, but it's defined in the middle of the (already very long) review view function. It should be refactored so it's defined as a property on the activity log classes instead (like other such properties are)

Acceptance Criteria

• addon_important_changes_actions built dynamically from the activity class constants

┆Issue is synchronized with this Jira Task