feat(api): Add is_bot to cffi and jsonrpc (#5197)

@adbenitez wants this feature on Deltalab to display a bot tag. 
Other UIs might also want to adopt this feature :)

---------
Co-authored-by: link2xt <link2xt@testrun.org>

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

@@ -45,6 +45,9 @@ pub struct ContactObject {
     /// the contact's last seen timestamp
     last_seen: i64,
     was_seen_recently: bool,
+
+    /// If the contact is a bot.
+    is_bot: bool,
 }
 
 impl ContactObject {
@@ -80,6 +83,7 @@ impl ContactObject {
             verifier_id,
             last_seen: contact.last_seen(),
             was_seen_recently: contact.was_seen_recently(),
+            is_bot: contact.is_bot(),
         })
     }
 }