Update delete button description in documentation and modify CLEAR_MESSAGES case to preserve message history

Author: vj-venkatesan

Diff for: docs/css-customization.md

@@ -1419,7 +1419,7 @@ The frame that adds the "card styles" such as background-color or box-shadow.
 ```
 
 - _webchat-delete-conversation-button_  
-  The general delete button style.
+  The delete button style inside the chat options screen.
 
 ```CSS
 [data-cognigy-webchat-root] .webchat-delete-conversation-button {

Diff for: src/webchat/store/messages/message-reducer.ts

@@ -308,7 +308,10 @@ export const createMessageReducer = (getState: () => { config: ConfigState }) =>
 				};
 			}
 			case CLEAR_MESSAGES: {
-				return [];
+				return {
+					...state,
+					messageHistory: [],
+				};
 			}
 			default:
 				return state;