Groovy DSL support for generator customizer

1. generatorCustomizer task property is now Groovy friendly!
   What previously had to be written as:

   tasks {
       generateJooqClasses(new MyCustomizer())
   }
   
   class MyCustomizer implements GeneratorCustomizer {
   
       @Override
       void execute(final Generator generator) {
           generator.database.withForcedTypes(...)
       }
   }

   now can be done in the closure directly in the task:

   tasks {
       generateJooqClasses {
           it.database.withForcedTypes(...)
       }
   }

2. New excludeFlywayTable task property to exclude the flyway_schema_history from generated classes:

   tasks {
       generateJooqClasses {
           excludeFlywayTable = true
       }
   }