feat: add "e2ee encrypted" info message to all e2ee chats (#7008)

this PR adds a info message "messages are end-to-end-encrypted" also for
chats created by eg. vcards. by the removal of lock icons, this is a
good place to hint for that in addition; this is also what eg. whatsapp
and others are doing

the wording itself is tweaked at
https://github.com/deltachat/deltachat-android/pull/3817 (and there is
also the rough idea to make the message a little more outstanding, by
some more dedicated colors)

~~did not test in practise, if this leads to double "e2ee info messages"
on secure join, tests look good, however.~~ EDIT: did lots of practise
tests meanwhile :)

most of the changes in this PR are about test ...

ftr, in another PR, after 2.0 reeases, there could probably quite some
code cleanup wrt set-protection, protection-disabled etc.

---------

Co-authored-by: Hocuri <hocuri@gmx.de>

src/test_utils.rs

@@ -43,6 +43,10 @@ use crate::securejoin::{get_securejoin_qr, join_securejoin};
 use crate::stock_str::StockStrings;
 use crate::tools::time;
 
+/// The number of info messages added to new e2ee chats.
+/// Currently this is "End-to-end encryption available", string `E2eAvailable`.
+pub const E2EE_INFO_MSGS: usize = 1;
+
 #[allow(non_upper_case_globals)]
 pub const AVATAR_900x900_BYTES: &[u8] = include_bytes!("../test-data/image/avatar900x900.png");