Bump Slf4j API to 2.0.x and drop support for Spring Boot 2

[linghengqian]

Feature Request

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Is your feature request related to a problem?

• For https://github.com/apache/shardingsphere-elasticjob/pull/2417 .

Describe the feature you would like.

• Bump Slf4j API to 2.0.x and drop support for Spring Boot 2. This obviously avoids defining something like the following in the relevant unit tests of Spring Boot 3.3.2.

  <properties>
      <spring-boot-dependencies.version>3.3.2</spring-boot-dependencies.version>
      <slf4j.version>2.0.13</slf4j.version>
      <logback.version>1.5.6</logback.version>
  </properties>

• But on the other hand, ShardingSphere itself is still using Slf4j API 1.7.36. And using Slf4j 2.0.x will indeed conflict with Spring Boot 2.x, refer to https://github.com/apache/shardingsphere/pull/29008 and https://github.com/spring-projects/spring-boot/issues/34708 .
• Open the current issue to discuss whether we should maintain support for Spring Boot 2.