Make `GenerateJavaTask.schemaPaths` lazy instead of `@Input List<Any>`

The schemaPaths input property of the GenerateJavaTask currently doesn't accept a Provider or a FileCollection.
If you resolve the graphql schema from an external dependency, that means you have to resolve that configuration at configuration time.
It is also a set of path string annotated with @Input rather than a set of files annotated with @InputFiles or @Classpath, so Gradle cannot determine whether files are up-to-date for task avoidance.
The plugin already does this correctly for the dgsCodegenClasspath ConfigurableFileCollection input in the same class annotated with @Classpath, making this inconsistent.

Can this be adjusted, so we can

• avoid configuration-time dependency resolution
• benefit from content-based up-to-date checking
• have type-safe input checking: a Set<File> accidentally passed as a single list element converted to the String literal [/path/to/schema.graphqls], brackets included, and the first sign of the mistake was a compilation failure in a downstream consumer.