Configures actor capture on a transition_log.
When present, AshWorkflow.Changes.RecordEvent sets this attribute on every
log row it writes to context.actor, following AshPaperTrail's
belongs_to_actor precedent rather than the library guessing an actor type.
With skip_other_actors?: true, an actor that is not a destination struct,
such as a plain-struct system actor, leaves the attribute nil.