move thumbnails to static assets

Author: ghidalgo3

public/images/hls2-l30-hero.webp

@@ -467,15 +467,13 @@ hgb:
 
 hls2-s30:
   category: Imagery
-  headerImg: ./images/hls2-s30-hero.webp
   tabs:
     - title: Example Notebook
       src: hls2-example.html
       launch: datasets/hls2/hls2-example.ipynb
 
 hls2-l30:
   category: Imagery
-  headerImg: ./images/hls2-l30-hero.webp
   tabs:
     - title: Example Notebook
       src: hls2-example.html