Move samples to dedicated modules

[Jérôme Wacongne]

Samples are currently mixed in test sources. This has the benefit of keeping jars small, but comes with quite a few drawbacks:

• it's hard to figure out what dependencies are pulled for samples or lib code
• users frequently just don't find samples
• non trivial spring-test conf is required just because several spring-boot apps share the same module

Let's create a samples module with a sub-module for each sample