Add ability to show string clip attributes as toggleable viewer overlays

[mvineeta]

Implement a viewer overlay system that allows users to toggle the display of any clip attribute of str (string) type (For example : 'Comment')

🎯 Feature Request:

Add a viewer overlay that displays a selected string-based clip attribute as simple text. For example, pressing the 'C' key would show the "Comment" attribute of the currently loaded clip as an overlay in the viewer.

✅ Expected Behavior:

• On pressing a shortcut key (e.g., 'C'):
  * The viewer shows the "Comment" attribute from the currently loaded clip.
  * Text appears in a small, readable format.
  * When the clip changes, the overlay updates dynamically with the new clip’s attribute.
  * If the attribute is missing or empty, the overlay hides or shows a placeholder (e.g., “No comment”).

• Should support any attribute of type str (not just "Comment"), making it extensible.

💡 Why It’s Useful:

• Quickly surfaces review notes, metadata, or custom strings.
• Improves on-screen readability during reviews without needing external tools or UI panels.

💻 Implementation Notes:

• Please make use of the existing HTML overlay API in RPA to render this overlay, rather than building a new system from scratch.
• Connect the overlay update mechanism to clip change events to ensure dynamic refresh.
• You can look into the existing media_path_overlay widget for reference — it already handles clip-related metadata display.
• Alternatively, you may rename and extend the media_path_overlay widget for this purpose, rather than creating a new widget from scratch.