feat: Add device message about outgoing undecryptable messages (#5164)

Currently when a user sets up another device by logging in, a new key is created. If a message is
sent from either device outside, it cannot be decrypted by the other device.

The message is replaced with square bracket error like this:
```
<string name="systemmsg_cannot_decrypt">This message cannot be decrypted.\n\n• It might already help to simply reply to this message and ask the sender to send the message again.\n\n• If you just re-installed Delta Chat then it is best if you re-setup Delta Chat now and choose "Add as second device" or import a backup.</string>
```
(taken from Android repo `res/values/strings.xml`)

If the message is outgoing, it does not help to "simply reply to this message". Instead, we should
add a translatable device message of a special type so UI can link to the FAQ entry about second
device. But let's limit such notifications to 1 per day. And as for the undecryptable message
itself, let it go to Trash if it can't be assigned to a chat by its references.

test-data/message/thunderbird_encrypted_signed.eml

@@ -9,8 +9,6 @@ User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Content-Language: en-US
 To: bob@example.net
 From: Alice <alice@example.org>
-X-Mozilla-Draft-Info: internal/draft; vcard=0; receipt=0; DSN=0; uuencode=0;
- attachmentreminder=0; deliveryformat=0
 X-Identity-Key: id3
 Fcc: imap://alice%40example.org@in.example.org/Sent
 Subject: ...