Fix dropzone visibility

[kwinto]

This pull request includes a minor update to the WebchatUI component in the src/webchat-ui/components/WebchatUI.tsx file. The change ensures that the drop zone visibility is only set when the file storage settings are enabled.

• src/webchat-ui/components/WebchatUI.tsx: Updated handleDragEnter to check if config?.settings?.fileStorageSettings?.enabled is true before calling this.props.onSetDropZoneVisible(true).

Success criteria

• When dragging a file into Webchat, we show the drop zone only when the file upload is configured.

How to test

1. Disable file upload in the endpoint
   Webchat3 -> Webchat behavior -> Attachment Upload -> Enabled: false
2. Try to drag a file into the Webchat. Drop zone should not be activated.
3. Enable file upload setting
4. Try to drag a file in.
5. Drop zone should become visible.

[Copilot]

Pull Request Overview

This PR updates the WebchatUI component to ensure that the drop zone is only activated when file upload is enabled in the settings.

• Updated the handleDragEnter function to conditionally show the drop zone based on the file storage settings.
• Removed an unused function (handleDropZoneVisibility) to clean up the code.