Create new version for Support Spring Boot 4.x line

[kazuki43zoo]

MyBatis Spring Boot 3.0.x does not work on Spring Boot 4.x line, because spring boot 4.x line does not keep compatibility with spring boot 3.x line (eg. such as spring-projects/spring-boot#46085).
Thefore we will create a new version such as 4.0 or 3.1. I prefer 4.0 for version affinity with spring boot.

[kazuki43zoo]

I has been pushed a new branch for developing 4.0.0. This branch will use until release the spring boot 4.0.0 GA.
After releasing spring boot 4.0.0, we will create 3.0.x branch for maintenance the 3.0.x line and merged it to master branch.

Branch: https://github.com/mybatis/spring-boot-starter/tree/4.0.x.dev