Rebuild the Examples to hold multiple variants; Boot 3, Bazel versions, Kotlin, etc.

[plaird]

Right now the examples are inline in the workspace with the rules_spring project itself. This is nice in that changes to the rule are instantly tested with the examples.

But we don't have a good way to test/demo it against:

• different versions of Bazel
• different versions of Spring Boot
• related tech stacks, like Kotlin, rules_oci etc

without making an absolute mess of the WORKSPACE file.

We will refresh the Kotlin branch in #183 but hopefully we build a better solution in this work.