feat: include Algolia in 404 search

wowchemy/layouts/404.html

@@ -5,7 +5,7 @@
   <h1>{{ i18n "page_not_found" }}</h1>
 
   {{/* Show search box if built-in search engine is enabled. */}}
-  {{ if eq (lower site.Params.search.provider) "wowchemy" }}
+  {{ if in (slice "wowchemy" "algolia") (lower site.Params.search.provider) }}
   <form class="d-flex align-items-center mb-3">
     <input name="q" type="search" class="form-control" placeholder="{{ i18n "search_placeholder" }}" autocomplete="off">
   </form>