[FEATURE REQ] Refactor Kafka support in Spring Cloud Azure

Now there are two authentication methods support in Spring Cloud Azure, one SASL plain, another is SASL connection string. The first will use the Event Hubs connection string, the second will use Microsoft Entra ID to auth.

But the implementation in Spring Cloud Azure is not consistent, and scattered in different autoconfiguration or BeanPostProcessors.

**Describe the solution you'd like**
Refactor the implemenataion to make the code easy to read and understand.

**Describe alternatives you've considered**
N/A
**Additional context**
N/A

**Information Checklist**
Kindly make sure that you have added all the following information above and checkoff the required fields otherwise we will treat the issuer as an incomplete report
- [x] Description Added
- [x] Expected solution specified