[FEATURE] Support Multiple PLAIN Authentication Methods Simultaneously

### 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/kyuubi/issues?q=is%3Aissue) and found no similar issues.

### Describe the feature
This feature request proposes enhancing Kyuubi to support multiple PLAIN authentication methods (e.g., LDAP and JDBC) concurrently, allowing greater flexibility for diverse use cases.

### Motivation
Currently, Apache Kyuubi supports SASL authentication with both KERBEROS and PLAIN (LDAP, JDBC, or CUSTOM) authentication types. However, when using PLAIN, only the first specified PLAIN authentication type is valid. This limitation prevents the simultaneous use of multiple PLAIN authentication methods, such as LDAP for user authentication and JDBC for ad-hoc jobs.

### Are you willing to submit PR?

- [ ] Yes. I would be willing to submit a PR with guidance from the Kyuubi community to improve.
- [x] No. I cannot submit a PR at this time.

Start by locating Kyuubi's SASL PLAIN authentication configuration and the implementation that currently accepts only the first configured method. Review the existing LDAP, JDBC, and CUSTOM authentication entry points and tests. Done means LDAP and JDBC can be enabled concurrently, with authentication behavior covered by tests.

Written by the indexing model from the issue text.