test: raft topology: test prepare_and_broadcast_cdc_generation_data

This test limits `commitlog_segment_size_in_mb` to 2, thus `max_command_size`
is limited to less than 1 MB. It adds an injection which copies mutations
generated by `get_cdc_generation_mutations` n times, where n is picked that
the memory size of all mutations exceeds `max_command_size`.

This test passes if cdc generation data is committed by raft in multiple commands.
If all the data is committed in a single command, the leader node will loop trying
to send raft command and getting the error:
```
storage_service - raft topology: topology change coordinator fiber got error raft::command_is_too_big_error (Command size {} is greater than the configured limit {})
```

test/topology_experimental_raft/test_cdc_generation_data.py

@@ -0,0 +1,31 @@
+from test.pylib.manager_client import ManagerClient
+from test.pylib.rest_client import inject_error
+from test.topology.util import check_token_ring_and_group0_consistency
+
+import pytest
+
+"""
+The injection forces the topology coordinator to send CDC generation data in multiple parts,
+if it didn't the command size would go over commitlog segment size limit making it impossible to commit and apply the command.
+"""
+@pytest.mark.asyncio
+async def test_send_data_in_parts(manager: ManagerClient):
+    config = {
+        'commitlog_segment_size_in_mb': 2
+    }
+
+    first_server = await manager.server_add(config=config)
+
+    async with inject_error(manager.api, first_server.ip_addr, 'cdc_generation_mutations_replication'):
+        await manager.server_add(config=config)
+
+    await check_token_ring_and_group0_consistency(manager)
+
+    cql = manager.get_cql()
+    rows = await cql.run_async("SELECT description FROM system.group0_history")
+
+    for row in rows:
+        if row.description.startswith('insert CDC generation data (UUID: ') and row.description.endswith('), part'):
+            break
+    else:
+        pytest.fail("No CDC generation data sent in parts was found")