[Cache] Add TLS scheme for Redis connection

See symfony/symfony#39599

Author: misaert

components/cache/adapters/redis_adapter.rst

@@ -62,15 +62,16 @@ helper method allows creating and configuring the Redis client class instance us
     );
 
 The DSN can specify either an IP/host (and an optional port) or a socket path, as well as a
-password and a database index.
+password and a database index. To enable TLS for connections, the scheme ``redis`` must be
+replaced by ``rediss``.
 
 .. note::
 
     A `Data Source Name (DSN)`_ for this adapter must use the following format.
 
     .. code-block:: text
 
-        redis://[pass@][ip|host|socket[:port]][/db-index]
+        redis[s]://[pass@][ip|host|socket[:port]][/db-index]
 
 Below are common examples of valid DSNs showing a combination of available values::