[kotlin-spring][server] Fix: treat "nullable: false, required: false" attributes with "default" fallback value as non-nullable in DTOs #217

Job	Run time
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-springboot-delegate-nodefaults)	2m 9s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-server-required-and-nullable-properties)	1m 46s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-springboot-additionalproperties)	1m 55s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-server/jaxrs-spec-mutiny)	1m 25s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-springboot-request-cookie)	2m 16s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-server/jaxrs-spec)	1m 28s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-springboot-3)	1m 57s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-server/ktor2)	2m 5s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-server/javalin)	1m 39s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-server/ktor)	1m 52s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-spring-declarative-interface-reactive...	2m 22s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-server/javalin-6)	1m 50s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-misk)	1m 53s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-spring-declarative-interface-reactive...	2m 16s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-spring-declarative-interface)	1m 50s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-spring-declarative-interface-wrapped)	2m 12s
	30m 55s

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