Check DKIM Authentication-Results (#3583)

Fix #3507

Note that this is not intended for a release at this point! We first have to test whether it runs stable enough. If we want to make a release while we are not confident enough in authres-checking, then we have to disable it.

BTW, most of the 3000 new lines are in `test_data/messages/dkimchecks...`, not the actual code

da3a4b94 adds the results to the Message info. It currently does this by adding them to `hop_info`. Maybe we should rename `hop_info` to `extra_info` or something; this has the disadvantage that we can't rename the sql column name though.

Follow-ups for this could be:
- In `update_authservid_candidates()`: Implement the rest of the algorithm @hpk42 and me thought about. What's missing is remembering how sure we are that these are the right authserv-ids. Esp., when receiving a message sent from another account at the same domain, we can be quite sure that the authserv-ids in there are the ones of our email server. This will make authres-checking work with buzon.uy, disroot.org, yandex.ru, mailo.com, and riseup.net.
- Think about how we present this to the user - e.g. currently the only change is that we don't accept key changes, which will mean that the small lock on the message is not shown.
- And it will mean that we can fully enable AEAP, after revisiting the security implications of this, and assuming everyone (esp. @link2xt who pointed out the problems in the first place) feels comfortable with it.

test-data/message/dkimchecks-2022-09-28/alice@fastmail.com/alice@hotmail.com

@@ -0,0 +1,45 @@
+ARC-Authentication-Results: i=2; mx2.messagingengine.com;
+    x-csa=none;
+    x-me-sender=none;
+    x-ptr=fail smtp.helo=EUR05-DB8-obe.outbound.protection.outlook.com
+    policy.ptr=mail-db8eur05olkn2101.outbound.protection.outlook.com;
+    bimi=skipped (DMARC Policy is not at enforcement);
+    arc=pass (as.1.microsoft.com=pass, ams.1.microsoft.com=pass)
+    smtp.remote-ip=40.92.89.101;
+    dkim=pass (2048-bit rsa key sha256) header.d=hotmail.com
+    header.i=@hotmail.com header.b=FbLQTic7 header.a=rsa-sha256
+    header.s=selector1 x-bits=2048;
+    dmarc=pass policy.published-domain-policy=none
+    policy.applied-disposition=none policy.evaluated-disposition=none
+    (p=none,d=none,d.eval=none) policy.policy-from=p
+    header.from=hotmail.com;
+    iprev=pass smtp.remote-ip=40.92.89.101
+    (mail-db8eur05olkn2101.outbound.protection.outlook.com);
+    spf=pass smtp.mailfrom=alice@hotmail.com
+    smtp.helo=EUR05-DB8-obe.outbound.protection.outlook.com
+Authentication-Results: mx2.messagingengine.com;
+    x-csa=none;
+    x-me-sender=none;
+    x-ptr=fail smtp.helo=EUR05-DB8-obe.outbound.protection.outlook.com
+      policy.ptr=mail-db8eur05olkn2101.outbound.protection.outlook.com
+Authentication-Results: mx2.messagingengine.com;
+    bimi=skipped (DMARC Policy is not at enforcement)
+Authentication-Results: mx2.messagingengine.com;
+    arc=pass (as.1.microsoft.com=pass, ams.1.microsoft.com=pass)
+      smtp.remote-ip=40.92.89.101
+Authentication-Results: mx2.messagingengine.com;
+    dkim=pass (2048-bit rsa key sha256) header.d=hotmail.com
+      header.i=@hotmail.com header.b=FbLQTic7 header.a=rsa-sha256
+      header.s=selector1 x-bits=2048;
+    dmarc=pass policy.published-domain-policy=none
+      policy.applied-disposition=none policy.evaluated-disposition=none
+      (p=none,d=none,d.eval=none) policy.policy-from=p
+      header.from=hotmail.com;
+    iprev=pass smtp.remote-ip=40.92.89.101
+      (mail-db8eur05olkn2101.outbound.protection.outlook.com);
+    spf=pass smtp.mailfrom=alice@hotmail.com
+      smtp.helo=EUR05-DB8-obe.outbound.protection.outlook.com
+ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=none; dmarc=none;
+ dkim=none; arc=none
+From: <alice@hotmail.com>
+To: <alice@fastmail.com>