only autofocus search form on hero header (#10489)

fixes #9701
fixes #10480

Author: b0o

app/components/header.hbs

@@ -10,7 +10,7 @@
         The Rust community’s crate registry
       </h1>
 
-      <SearchForm @size={{if @hero "big"}} />
+      <SearchForm @size={{if @hero "big"}} @autofocus={{@hero}} />
     </div>
 
     <nav local-class='nav'>

app/components/search-form.hbs

@@ -26,7 +26,7 @@
     placeholder="Type 'S' or '/' to search"
     value={{this.header.searchValue}}
     oninput={{this.updateSearchValue}}
-    autofocus="autofocus"
+    autofocus={{@autofocus}}
     required
     aria-label="Search"
     data-test-search-input