Feat: Add Search Instruction on Search Messages Sidebar

[dhairyashiil]

As an EmbeddedChat developer

I need to: add a search instruction section to the sidebar when the "Search Messages" view is active, explaining how users can search using regular expressions.

So That: users can easily understand how to use advanced search functionality via regular expressions.

Acceptance Criteria

• Instruction Display: When the view type is "Search Messages", a section with a markdown formatted message appears at the top of the sidebar.
• Styling: The instruction should have its own custom style handling dark and light themes.
• Rendering Condition: The instruction should only be rendered when the title of the view is Search Messages.

Refer RC: