feat: Group and broadcast channel descriptions (#7829)

fix https://github.com/chatmail/core/issues/7766

Implementation notes:

- Descriptions are only sent with member additions, when the description
is changed, and when promoting a previously-unpromoted group, in order
not to waste bandwith.
- Descriptions are not loaded everytime a chat object is loaded, because
they are only needed for the profile. Instead, they are in their own
table, and can be loaded with their own JsonRPC call.

---------

Co-authored-by: iequidoo <117991069+iequidoo@users.noreply.github.com>

src/sql/migrations.rs

@@ -1558,6 +1558,15 @@ ALTER TABLE contacts ADD COLUMN name_normalized TEXT;
         .await?;
     }
 
+    inc_and_check(&mut migration_version, 147)?;
+    if dbversion < migration_version {
+        sql.execute_migration(
+            "CREATE TABLE chats_descriptions (chat_id INTEGER PRIMARY KEY AUTOINCREMENT, description TEXT NOT NULL DEFAULT '') STRICT;",
+            migration_version,
+        )
+        .await?;
+    }
+
     let new_version = sql
         .get_raw_config_int(VERSION_CFG)
         .await?