[SCS-MultiApi-Plugin] [OpenApi] Fix TemplateSchema CollectionUtils.isNotEmpty Import

[Rivarsal]

Currently, there is an small Bug in the TemplateSchema.ftlh where the generatedFile uses the method CollectionUtils.isNotEmpty but it does not have the import added.

As a developer must I want the dependency added from Maven aswell as the logic needed in order to import CollectionUtils dinamycally. Here is the maven repository:

https://mvnrepository.com/artifact/org.apache.commons/commons-collections4