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)

---------

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

src/stock_str.rs

@@ -419,6 +419,11 @@ pub enum StockMessage {
 
     #[strum(props(fallback = "Member %1$s added."))]
     MsgAddMember = 173,
+
+    #[strum(props(
+        fallback = "⚠️ Your email provider %1$s requires end-to-end encryption which is not setup yet."
+    ))]
+    InvalidUnencryptedMail = 174,
 }
 
 impl StockMessage {
@@ -1285,6 +1290,13 @@ pub(crate) async fn aeap_addr_changed(
         .replace3(new_addr)
 }
 
+/// Stock string: `⚠️ Your email provider %1$s requires end-to-end encryption which is not setup yet. Tap to learn more.`.
+pub(crate) async fn unencrypted_email(context: &Context, provider: &str) -> String {
+    translated(context, StockMessage::InvalidUnencryptedMail)
+        .await
+        .replace1(provider)
+}
+
 pub(crate) async fn aeap_explanation_and_link(
     context: &Context,
     old_addr: &str,