Create the ModerationDecision admin views

[stacimc]

Description

Blocked by #3636

Create a Django admin ListView for the ModerationDecision model, for viewing historical ModerationDecisions. In the list view we should sort decisions by creation date and display:

• id
• action
• explanation (truncated)
• record_count - a count for the number of records affected by the decision

The view should have a custom filter to display only bulk moderation decisions, defined as a ModerationDecision with more than one media record.

Also include a read-only detail view for individual ModerationDecisions when selected from the list. For ModerationDecisions with a deindexed_sensitive, deindexed_copyright, or marked_sensitive action type, include a link to the SensitiveMedia or DeletedMedia view, filtered by the ModerationDecision id for convenience.

Additional context

See IP for details.