Store type property no longer exists

[jpmsilva]

Describe the bug
The documentation pages at https://docs.spring.io/spring-session/reference/guides/boot-redis.html and https://docs.spring.io/spring-session/reference/guides/boot-jdbc.html (and possibly others) reference the Spring Boot property spring.session.store-type.

This property no longer exists as seen in spring-projects/spring-boot#27756. It was replaced with an implicit order for store types.

The documentation may need to be updated to reflect this change.