This commit reorganizes tasks and scripts in the build to only apply
them where they're needed. We're considering here 3 "types" of projects
in our build:
* the root project, handling documentation, publishing, etc
* framework modules (a project that's published as a spring artifact)
* internal modules, such as the BOM, our coroutines support and our
integration-tests
With this change, we're strealining the project configuration for all
spring modules and only applying plugins when needed (typically our
kotlin support).
See gh-23282
The main `build.gradle` file contains now only the common build
infrastructure; all module-specific build configurations have
been moved to their own build file.
Issue: SPR-15885
