Having a transparent background in case there's a rendering issue in the knowledge panels

[teolemon]

What

• Image not rendered in the "Threatened Species" sub-sub-panel #1023 and Image not rendered in the alcohol panel #1013 are examples of what happens if for some reason we're not able to render a panel
• Having a transparent background in case there's a rendering issue in the knowledge panels would be more gracious for the user
• To ensure we can still debug, we could enable changing back to grey in dev mode
• We should ensure the proper exceptions are raised and sent to Sentry

Part of

• 📖 Knowledge panels (Tracker) #499