Upgrade maestro server example to use Springboot3

[jun-he]

Should upgrade it based on https://spring.io/projects/spring-boot#support

[mroyme]

Hi, @jun-he
I created a PR to fully upgrade spring-boot to 3.3.x. It's a big PR, although the changes are kind of repetitive, like replacing javax packages with jakarta ones. So, please take a look whenever you can. #58

Cheers! :)

[jun-he]

@mroyme Thanks for the PR. As you discovered, it needs a few prerequisite changes, e.g. #5 #10.