The spec should clarify whether push rules for a user should be executed against their own events

**Link to problem area**: https://spec.matrix.org/v1.5/client-server-api/#push-rules

**Issue**
Presumably users should not be sent a push notification when their own messages happen to match their defined push rules, but this is not explicitly stated in the spec.

Synapse does not evaluate notification actions for a user if they are the sender of the event: https://github.com/matrix-org/synapse/blob/33e6e916dc0f79aad770961634ad5e1f32945cf8/synapse/push/bulk_push_rule_evaluator.py#L362-L363

Start with the linked Matrix client-server API push-rules section and review the linked Synapse evaluator behavior. Clarify in the specification whether a user's push rules apply to events they sent, with wording that makes the expected behavior explicit.

Written by the indexing model from the issue text.