Provide a way to disable/control cleanup cron

[saiya]

Provide following features on Redis and JDBC backend (discussed in #1159).

• Way to stop cleanup cron (set cleanupCron = "disabled")
• Enable to use property placeholder within cleanupCron attribute

This resolves #1159.

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[saiya]

Thank you for taking this issue @vpavic .

If there anything I can/should do for this PR, please tell me 👍

[vpavic]

Thanks for the PR @saiya, however we'd like to reuse Spring Framework's Scheduled#CRON_DISABLED as a special value to disable session cleanup scheduled job.

Looks like that's going to require some changes in the Framework - see spring-projects/spring-framework#23568.

[vpavic]

With spring-projects/spring-framework#23568 resolved, starting Spring Session 2.2.0.RC1 it should be possible to disable the cleanup job using Scheduled#CRON_DISABLED for cron value.