fix(CDC_OPTIONS): Use boolean value for cdc preimage option

CDC_SETTINGS_NAMES_VALUES['preimage'] uses string values "true" "false"
instead of bool True False. This cause assertion error if it was changed

```
AssertionError: CDC extension settings are differs.
Current: {'delta': 'full', 'enabled': True, 'preimage': True, 'postimage': True, 'ttl': '1800'}
expected: {'delta': 'full', 'enabled': True, 'preimage': 'true', 'postimage': True, 'ttl': '1800'}
```

sdcm/utils/cdc/options.py

@@ -11,7 +11,7 @@
 CDC_SETTINGS_NAMES_VALUES = {
     "enabled": [True, False],
     "delta": ["full", "keys"],
-    "preimage": ["full", "true", "false"],
+    "preimage": ["full", True, False],
     "postimage": [True, False],
     "ttl": "86400"
 }