### _Why are the changes needed?_
Add `_configurations` in kerberos.rst
### _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
- [x] [Run test](https://kyuubi.readthedocs.io/en/master/develop_tools/testing.html#running-tests) locally before make a pull request
Closes#4362 from Yikf/kerberos-doc-config.
Closes#4362
d8f197642 [Yikf] Add _configurations in kerberos.rst
Authored-by: Yikf <yikaifei@apache.org>
Signed-off-by: liangbowen <liangbowen@gf.com.cn>