FEATURE: add support for fluid ad size in Google Ad Manager

No width or height will be set on containers when ad size is fluid.

assets/javascripts/discourse/components/google-dfp-ad.js.es6

@@ -126,6 +126,10 @@ function getWidthAndHeight(placement, settings, isMobile) {
     renderCounts[placement] += 1;
   }
 
+  if (size === "fluid") {
+    return { width: 'fluid', height: 'fluid' };
+  }
+
   const sizeObj = {
     width: parseInt(splitWidthInt(size), 10),
     height: parseInt(splitHeightInt(size), 10)
@@ -281,12 +285,16 @@ export default AdComponent.extend({
 
   @computed("width", "height")
   adWrapperStyle(w, h) {
-    return `width: ${w}px; height: ${h}px;`.htmlSafe();
+    if (w !== 'fluid') {
+      return `width: ${w}px; height: ${h}px;`.htmlSafe();
+    }
   },
 
   @computed("width")
   adTitleStyleMobile(w) {
-    return `width: ${w}px;`.htmlSafe();
+    if (w !== 'fluid') {
+      return `width: ${w}px;`.htmlSafe();
+    }
   },
 
   @computed(