Fluentd: How to use env variable in record config

Question

I have a container which has a env variable set:

env['POD_NAME'] = 'some-pod-name'

Now, I want to use it while setting a json object in record:

<parse>
     @type openmetrics
     <record>
       namespace ns1
       resourceGroup rg1
       dimensions {"a": "1234", "b": "xyz", "node": "#{ENV['POD_NAME']}"}
    </record> 
</parse>