feat: Add more granular controls for policy server calling (#1127)

Adds two new toggles to the configuration, the first of which allows disabling the policy server checks entirely, and the second of which allows disabling checking events created locally. They're both enabled by default for maximum PS efficacy but allowing them to be disabled allows people who frequently cannot contact policy servers, for example those in censored countries, to be able to still use rooms with pace, allows single-user/trusted-only homeservers to disable the preliminary check on their own events, and also gives an escape hatch in case an issue like #1060 happens again, especially with MSCs not in FCP being moving targets.

In future, I think we should gate all MSC implementations behind config flags, even if they default to on.

Reviewed-on: https://forgejo.ellis.link/continuwuation/continuwuity/pulls/1127
Reviewed-by: Jade Ellis <jade@ellis.link>
Co-authored-by: timedout <git@nexy7574.co.uk>
Co-committed-by: timedout <git@nexy7574.co.uk>

src/service/rooms/event_handler/policy_server.rs

@@ -31,6 +31,19 @@ pub async fn ask_policy_server(
 	pdu_json: &CanonicalJsonObject,
 	room_id: &RoomId,
 ) -> Result<bool> {
+	if !self.services.server.config.enable_msc4284_policy_servers {
+		return Ok(true); // don't ever contact policy servers
+	}
+	if self.services.server.config.policy_server_check_own_events
+		&& pdu.origin.is_some()
+		&& self
+			.services
+			.server
+			.is_ours(pdu.origin.as_ref().unwrap().as_str())
+	{
+		return Ok(true); // don't contact policy servers for locally generated events
+	}
+
 	if *pdu.event_type() == StateEventType::RoomPolicy.into() {
 		debug!(
 			room_id = %room_id,