<!--

Welcome to Apache Airflow!  For a smooth issue process, try to answer the following questions.
Don't worry if they're not all applicable; just try to include what you can :-)

If you need to include code snippets or logs, please put them in fenced code
blocks.  If they're super-long, please use the details tag like
<details><summary>super-long log</summary> lots of stuff </details>

Please delete these comment blocks before submitting the issue.

-->

**Description**

In Spark Kubernetes operator we have hard-coded API group and version for spark application k8s object:
https://github.com/apache/airflow/blob/b23a4cd6631ba3346787b285a7bdafd5e71b43b0/airflow/providers/cncf/kubernetes/operators/spark_kubernetes.py#L63-L65
I think it is not good, because we can have situation that some custom or not opensource Spark k8s operators can have different API group and version (like `sparkoperator.mydomain.com` instead of `sparkoperator.k8s.io`). 
<!-- A short description of your feature -->

**Use case / motivation**

User have got installed custom or commercial Spark Kubernetes operator and he wants to launch DAG with `SprkKubernetesOperator` from providers. User cannot do that without this implemented feature.

<!-- What do you want to happen?

Rather than telling us how you might implement this solution, try to take a
step back and describe what you are trying to achieve.

-->

**Are you willing to submit a PR?**

Yes
<!--- We accept contributions! -->

**Related Issues**

No
<!-- Is there currently another issue associated with this? -->

tests/providers/cncf/kubernetes/operators/test_spark_kubernetes.py
"kind":"SparkApplication",
   "metadata":{
      "name":"spark-pi",
      "namespace":"default"
   },
   "spec":{
      "type":"Scala",
      "mode":"cluster",
      "image":"gcr.io/spark-operator/spark:v2.4.5",
      "imagePullPolicy":"Always",
      "mainClass":"org.apache.spark.examples.SparkPi",
      "mainApplicationFile":"local:///opt/spark/examples/jars/spark-examples_2.11-2.4.5.jar",
      "sparkVersion":"2.4.5",
      "restartPolicy":{
         "type":"Never"
      },
      "volumes":[
         {
            "name":"test-volume",
            "hostPath":{
               "path":"/tmp",
               "type":"Directory"
            }
         }
      ],
      "driver":{
         "cores":1,
         "coreLimit":"1200m",
         "memory":"512m",
         "labels":{