### _Why are the changes needed?_
Add `Kyuubi Deploy On Kubernetes ServiceAccount-related` documentation, and explicitly assert serviceAccountName: default as the default configuration in the template file `${KYUUBI_HOME}/docker/kyuubi-pod(deployment).yaml` to make it easier for users to set.
### _How was this patch tested?_
- [ ] Add some test cases that check the changes thoroughly including negative and positive cases if possible
- [ ] Add screenshots for manual tests if appropriate
- [ ] [Run test](https://kyuubi.apache.org/docs/latest/develop_tools/testing.html#running-tests) locally before make a pull request
Closes#3906 from zwangsheng/doc/kyuubi_on_k8s_service_account.
Closes#3902
e0ed06d6 [Cheng Pan] Update docs/deployment/kyuubi_on_kubernetes.md
6cd29dd0 [zwangsheng] build doc for serviceAccount
Lead-authored-by: zwangsheng <2213335496@qq.com>
Co-authored-by: Cheng Pan <pan3793@gmail.com>
Signed-off-by: Cheng Pan <chengpan@apache.org>
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