FEATURE: allow search engines to index tag pages. (#12248)

Previously, we blocked search engines in tag pages since they may get marked as a duplicate content.

* DEV: block tag inner pages from search engines crawling.

spec/requests/tags_controller_spec.rb

@@ -29,7 +29,6 @@ describe TagsController do
         tags = response.parsed_body["tags"]
         expect(tags.length).to eq(1)
         expect(tags[0]['text']).to eq("topic-test")
-        expect(response.headers['X-Robots-Tag']).to eq('noindex')
       end
     end