message deletion request API (#6576)

this PR adds an API allowing users to delete their messages on other
member's devices

this PR is build on top of
https://github.com/deltachat/deltachat-core-rust/pull/6573 which should
be merged first

a test is missing, otherwise ready for review; it is working already in
https://github.com/deltachat/deltachat-ios/pull/2611

src/mimeparser.rs

@@ -292,6 +292,7 @@ impl MimeMessage {
                     if !headers.contains_key(&key)
                         && (key == "chat-user-avatar"
                             || key == "chat-group-avatar"
+                            || key == "chat-delete"
                             || key == "chat-edit")
                     {
                         headers.insert(key.to_string(), field.get_value());
@@ -450,6 +451,7 @@ impl MimeMessage {
                     HeaderDef::ChatGroupMemberAdded,
                     HeaderDef::ChatGroupMemberTimestamps,
                     HeaderDef::ChatGroupPastMembers,
+                    HeaderDef::ChatDelete,
                     HeaderDef::ChatEdit,
                 ] {
                     headers.remove(h.get_headername());