Add filter to exclude non-docs domains from search results (#1277)

As part of [min.io issue
#2136](https://github.com/miniohq/min.io/issues/2136), the crawler now
includes results from domains such as blog.min.io and resource.min.io.
By default, the search returns results from all these sources. This
update adds a filter to exclude results from domains other than
docs.min.io.

Also, added some minor CSS changes to fix the gray color palette
variables.

source/_static/js/instantSearch.js

@@ -104,6 +104,7 @@ window.addEventListener("DOMContentLoaded", () => {
       minio: {
         refinementList: {
           platform: [activePlatform],
+          site: "docs"
         },
       },
     },
@@ -286,6 +287,9 @@ window.addEventListener("DOMContentLoaded", () => {
         },
       },
     }),
+    instantsearch.widgets.configure({
+      filters: `site:docs`, 
+    })
   ]);
 
   // Function to clear search field and filters