[Subtask #2444] Add kyuubi.backend.application.manager.classes for configuring ApplicationOperations

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)

### Search before asking

- [X] I have searched in the [issues](https://github.com/apache/incubator-kyuubi/issues) and found no similar issues.

### Describe the subtask

add a conf named kyuubi.backend.application.manager.classes for configuring `ApplicationOperation` s

### Parent issue

#2444

### Are you willing to submit PR?

- [ ] Yes I am willing to submit a PR!

Start with parent issue #2444 and search the repository for ApplicationOperation and existing kyuubi.backend.application.manager configuration names. Trace how application manager classes are loaded and review nearby configuration tests if present. Done means the new kyuubi.backend.application.manager.classes setting is recognized and configures ApplicationOperations as intended.

Written by the indexing model from the issue text.