add self-start class to interactive image panel

[RyanCoulsonCA]

Related Item(s)

https://github.com/ramp4-pcar4/tcei-tmx-cwa-storylines/issues/187

Changes

• Adds the self-start class to the image section of the interactive image panel. This will make it scroll down with the page if the text panel exceeds the height of the window.

Testing

Steps:

1. Open the demo link.
2. Make the window width just large enough that you don't go into mobile view (just around 650px).
3. Scroll down to the "Interactive image test" slide.
4. Click on the interactive box on the right side of the image and a bunch of Lorem Ipsum text should show up.
5. Scroll up and down to view the text, and ensure the image on the left side is fixed to the top of the screen as you scroll.

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This change is 

[github-actions]

Your demo site is ready! 🚀 Visit it here: https://ramp4-pcar4.github.io/story-ramp/fix-187/#/en/00000000-0000-0000-0000-000000000000