Update sample.batch.sleepybatchlet to support batch-2.1(Jakarta EE 10)

[blueangie]

We have a client asking for an updated sample.batch.sleepybatchlet to support batch-2.1(Jakarta EE 10), which they need for an upgrade.

Case number is TS022304490

[scottkurz]

I did an example of EE 8 -> 10, along with a couple other upgrades like upgrading liberty-maven-plugin so you can use dev mode, at this branch: https://github.com/scottkurz/sample.batch.sleepybatchlet/tree/batch-2.1-example