Update samples to use SB3/SF6

[onobc]

Lets go through the samples and be sure they are up-to-date on SB/SF as well as any other code usages etc.. This will be one of the 1st places people dig into.

[onobc]

The SpringBoot plugin was in fact set to 2.7.2 but it has no bearing on the final runtime as Gradle dependency version alignment kicks in and the later SB pulled in by spring-pulsar-depenencies is what is actually used at runtime.

IOW - the samples are running on SB3/SF6.