[CW-2688] Open chat widget with placeholder message

### Is your feature or enhancement related to a problem? Please describe.

We have some CTAs that lead to support, that require manual intervention on our side.

### Describe the solution you'd like

It would be nice to be able to open the widget with a predefined message, just like WhatsApp allows in its links:

`https://wa.me/1XXXXXXXXXX?text=I'm%20interested%20in%20your%20car%20for%20sale`

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

_{[CW-2688](https://linear.app/chatwoot/issue/CW-2688/open-chat-widget-with-placeholder-message)}