feat: Add system message when provider does not allow unencrypted messages (#5161) (#5195)

close #5161

![Screenshot from 2024-01-19
19-56-09](https://github.com/deltachat/deltachat-core-rust/assets/39526136/27ecdd9b-1739-410b-bb26-80d5bdbbc39a)

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Co-authored-by: bjoern <r10s@b44t.com>

deltachat-jsonrpc/src/api/types/message.rs

@@ -345,6 +345,7 @@ pub enum SystemMessageType {
     SecurejoinMessage,
     LocationStreamingEnabled,
     LocationOnly,
+    InvalidUnencryptedMail,
 
     /// Chat ephemeral message timer is changed.
     EphemeralTimerChanged,
@@ -385,6 +386,7 @@ impl From<deltachat::mimeparser::SystemMessage> for SystemMessageType {
             SystemMessage::MultiDeviceSync => SystemMessageType::MultiDeviceSync,
             SystemMessage::WebxdcStatusUpdate => SystemMessageType::WebxdcStatusUpdate,
             SystemMessage::WebxdcInfoMessage => SystemMessageType::WebxdcInfoMessage,
+            SystemMessage::InvalidUnencryptedMail => SystemMessageType::InvalidUnencryptedMail,
         }
     }
 }