Add the functionality to add a new note

#### Description:
Currently, when the user clicks the plus icon to add a new note, no note is being created. The functionality to handle the addition of new notes is not implemented in the controller.

#### Tasks:
1. **Implement Note Creation Function in the Controller:**
- Create a function that handles the logic for adding a new note, including input validation and state management.

2. **Integrate the Function:**
- Connect the newly implemented function to the event handler for the plus icon, ensuring that clicking the icon triggers the creation of a new note.

3. **Testing:**
- Verify that new notes are successfully created and displayed after the user interacts with the plus icon.

#### Expected Outcome:
When a user clicks the plus icon, a new note should be added and displayed in the notes list.