title: Adding normalizer for all keyword fields NEST
body: <p>I am able to set up a normalizer on a keyword mapping in NEST using the following:</p>
  
  <pre><code>   client.Indices.Create(indexName, c =&gt; c
          .Map&lt;Item&gt;(m =&gt; m.Properties(ps =&gt; ps
            .Text(s =&gt; s
              .Name(new PropertyName("someProp"))
              .Fields(f =&gt; f
                .Keyword(kw =&gt; kw
                  .Name("keyword")
                  .Normalizer("my_normalizer")
                )
              )
            )
          )
        )
  </code></pre>
  
  <p>Is there a way to add the normalizer across all keyword fields for a specified mapping without declaring all of the fields? I have looked into the property visitor pattern and used AutoMap however I didn't have much luck as anything set in these seems to be overwritten, perhaps this isn't the right place to do this?</p>