feat(Img): update image options

- set showCaptions to only title, as we don't want captions for alt text only images
- set markdownCaptions to allow for rich-text in captions
- disableBgImageOnAlpha to fix blurry edges on transparent pngs
- enable webP when isOnline

gatsby-config.js

@@ -122,7 +122,10 @@ const plugins = [
             maxWidth: 800,
             backgroundColor: `#eae9e9`,
             linkImagesToOriginal: false,
-            showCaptions: true,
+            showCaptions: [`title`],
+            markdownCaptions: true,
+            disableBgImageOnAlpha: true,
+            withWebp: isOnline,
             quality: 75,
             wrapperStyle: f => `flex:${round(f.aspectRatio, 2)};`,
             ignoreFileExtensions: [], // the quick fix? #6698