title: Create custom grok pattern to message filed in elasticsearch
body: <p>I am having a query related to grok processor. 
  For example this is my message filed </p>
  
  <pre><code>{
  "message":"agentId:agent003"
  }
  </code></pre>
  
  <p>I want to Grok this and my output should me something like this</p>
  
  <pre><code>{
  "message":"agentId:agent003",
  "agentId":"agent003"
  }
  </code></pre>
  
  <p>Could some one help me on this how to achieve this? If i am able to do it for one field i can manage for rest of my fields. Thanks in advance.</p>
  
  <p><strong>This is the pipeline i have created in elasticsearch</strong></p>
  
  <pre><code>PUT _ingest/pipeline/dissectpipeline
  {
    "description" : "split message content",
    "processors": [
      {
        "dissect": {
        "field": "message",
        "pattern" : "%{apm_application_message.agentId}:%{apm_application_message.agentId}"
     }
      }
    ]
  }
  </code></pre>
  
  <p><strong>Central management added filebeat module other config</strong></p>
  
  <pre><code>- pipeline:
      if: ctx.first_char == '{'
      name: '{&lt; IngestPipeline "dissectpipeline" &gt;}'
  </code></pre>
  
  <p>There is no error with my filebeat it's working fine but i am unable to find any field like apm_application_message.agentId in index.</p>
  
  <p>How to make sure my pipeline working or not. Also if i am doing something wrong please let me know.</p>