title: Add synonym analyzer to elasticsearch index
body: <p>i have an existing elasticsearch index and i would like to add a analyzer but when i execute this command </p>
  
  <pre><code>{
  "analysis" : {
      "analyzer" : {
          "synonym" : {
              "tokenizer" : "whitespace",
              "filter" : ["synonym"]
          }
      },
  "filter" : {
              "synonym" : {
                  "type" : "synonym",
                  "synonyms_path" : "synonym.txt",
                  "ignore_case" : true
              }
          }
      }
  }
  </code></pre>
  
  <p>i get an error </p>
  
  <blockquote>
    <p>{"error":"IndexAlreadyExistsException[[nuxeo] already exists]","status":400}</p>
  </blockquote>
  
  <p>so i have to remove the index before add or refresh the synonym file is not very smart 
  A simply way exist to add a analyzer ? or at least to refresh it? thanks</p>