elastic-package format to convert dotted configurations to objects

[jsoriano]

In Package Spec v3 dotted notation is not allowed in YAML files, and nested settings must be defined in nested objects, see elastic/package-spec#538.

Make elastic-package format capable to automatically convert between the dotted notation and the nested objects for packages using the newest versions of Package Spec. For the rest it must keep the format of the file.

The way to do this manually is described in https://github.com/elastic/elastic-package/blob/main/docs/howto/update_major_package_spec.md#field--additional-property--is-not-allowed