title: Can we use "oneOf" in Confluent Platform Schema Registry?
body: <p>I have a use case of user balance changes. I want to put all user balance events in 1 topic. But user balance changes are happening due to multiple events like referral bonus, win bonus, withdrawal, deposit. This can be implemented via nested records like this :</p>
  
  <pre><code>{
  "name": "userBalance",
  "type": "record",
  "fields": [
         {
              "name": "cashDeposit",
              "type": 
                     {
                          "type" : "record",
                          "name" : "userCashDeposit",
                          "fields" : [
                              {"name": "id", "type": "long"},
                              {"name": "amount", "type": "float"}
                          ]
                      }
          },
          {
              "name": "cashWithdraw",
              "type": {
                          "type" : "record",
                          "name" : "userCashWithdraw",
                          "fields" : [
                              {"name": "id", "type": "long"},
                              {"name": "amount", "type": "float"}
                          ]
                      }
          }
      ]
  }
  </code></pre>
  
  <p>But this makes all the nested records as required, while I want to strictly implement that any <strong>one of</strong> these events be present in the event with strict compliance to that events' record.  Avro schema supports "oneOf" but I could not find oneOf being used anywhere for Confluent Schema Registry usecase. Is there any way to use it?</p>