doc: enabling experimental Raft-managed topology

This commit adds a short paragraph to the Raft
page to explain how to enable consistent
topology updates with Raft - an experimental
feature in version 5.4.

The paragraph should satisfy the requirements
for version 5.4. The Raft page will be
rewritten in the next release when consistent
topology changes with Raft will be GA.

Fixes https://github.com/scylladb/scylladb/issues/15080

Requires backport to branch-5.4.

Closes scylladb/scylladb#16273

docs/architecture/raft.rst

@@ -219,6 +219,36 @@ of nodes in the cluster is available. The following examples illustrate how Raft
 
 In summary, Raft makes schema changes safe, but it requires that a quorum of nodes in the cluster is available.
 
+.. _raft-topology-changes:
+
+.. only:: opensource
+
+    Consistent Topology with Raft :label-caution:`Experimental`
+    -----------------------------------------------------------------
+
+    ScyllaDB can use Raft to manage cluster topology. With Raft-managed topology 
+    enabled, all topology operations are internally sequenced in a consistent 
+    way. A centralized coordination process ensures that topology metadata is 
+    synchronized across the nodes on each step of a topology change procedure. 
+    This makes topology updates fast and safe, as the cluster administrator can 
+    trigger many topology operations concurrently, and the coordination process 
+    will safely drive all of them to completion. For example, multiple nodes can 
+    be bootstrapped concurrently, which couldn't be done with the old 
+    gossip-based topology.
+
+    Support for Raft-managed topology is experimental and must be explicitly 
+    enabled in the ``scylla.yaml`` configuration file by specifying 
+    the ``consistent-topology-changes`` option:
+
+    .. code:: 
+    
+        experimental_features:
+        - consistent-topology-changes
+
+    As with other experimental features in ScyllaDB, you should not enable this 
+    feature in production clusters due to insufficient stability. The feature 
+    is undergoing backward-incompatible changes that may prevent upgrading 
+    the cluster. 
 
 .. _raft-handling-failures: