Migration to SpringBoot 3.x

[roskenet]

When trying to use the starter in a SpringBoot 3.x project I found the following issues:

1. The class for autoconfig is not processed (now META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports)

2. The FlywayMigrator doesn't work anymore due to the change in the import of the PostConstruct annotation using jakarta.* instead of javax.* in SpringBoot 3.

Besides that I haven't found any issues yet (after importing the autoconfig class by hand).
Bumping up the SpringBoot version in nakadi-producer-starter breaks all the tests. (Needs a bit deeper trouble-shooting).

[ePaul]

@roskenet Do you still intend to look into this so we can release a springboot-3-compatible version?

[wormangel]

@roskenet Do you still intend to look into this so we can release a springboot-3-compatible version?

I'm working on a PR right now, continuing where #189 left off and taking into account @roskenet's input above.