Use frontpage images (#18718)

source/blue/index.html

@@ -22,6 +22,7 @@ tagline: >-
     </svg>
 tagline_wide: false
 og_image: /images/blue/blue_hero.jpg
+frontpage_image: /images/frontpage/blue-frontpage.jpg
 ---
 
 <div class="content">

source/home-energy-management/index.html

@@ -5,6 +5,7 @@ date: 2021-07-28
 description: "Monitor your energy usage, transition to sustainable energy and save money"
 hero_image: /images/energy/hero.jpg
 og_image: /images/blog/2021-08-energy/social.png
+frontpage_image: /images/frontpage/energy-frontpage.jpg
 tagline: The world is heating up. Together we can fix that.
 sections:
   - title: "Monitor usage"

source/index.html

@@ -95,7 +95,7 @@ feedback: false
           class="material-card picture-promo"
           href="{{page.url}}"
           style="
-            background-image: url({{page.hero_image | default:page.og_image}});
+            background-image: url({{page.frontpage_image | default:page.og_image}});
             background-size: cover;
             background-color: #41bdf5;
           "