feat: Save the secret to encrypt and decrypt messages. Next: Send it in a 'member added' message.

src/sql/migrations.rs

@@ -1264,10 +1264,13 @@ CREATE INDEX gossip_timestamp_index ON gossip_timestamp (chat_id, fingerprint);
     inc_and_check(&mut migration_version, 134)?;
     if dbversion < migration_version {
         sql.execute_migration(
-            "CREATE TABLE symmetric_secrets(
-            chat_id INTEGER PRIMARY KEY NOT NULL,
-            symmetric_secret: ",
+            "CREATE TABLE broadcasts_shared_secrets(
+                chat_id INTEGER PRIMARY KEY NOT NULL, -- TODO we don't actually need the chat_id
+                secret TEXT NOT NULL
+            ) STRICT",
+            migration_version,
         )
+        .await?;
     }
 
     let new_version = sql