Chat: Add Suggestions Demo Desc. (#33361)

Author: arman-boyakhchyan

apps/demos/Demos/Chat/PromptSuggestions/description.md

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+DevExtreme [Chat](/Documentation/Guide/UI_Components/Chat/Overview/) supports [suggestions](/Documentation/ApiReference/UI_Components/dxChat/Configuration/#suggestions) - hints that guide users throughout conversations. The component displays suggestion buttons above the message input field and supports both persistent and temporary hints.
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+<!--split-->
+This demo allows you to configure suggestions as follows:
+
+- Specify whether the Chat displays a predefined prompt in the [input field](/Documentation/ApiReference/UI_Components/dxChat/Configuration/#inputFieldText) or immediately sends a message with that prompt.
+- Enable single-use suggestions.