[kotlin-spring][server] Fix: treat "nullable: false, required: false" attributes with "default" fallback value as non-nullable in DTOs #196

Job	Run time
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-springboot-delegate-nodefaults)	1m 56s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-springboot-3)	2m 14s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-springboot-additionalproperties)	2m 28s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-springboot-request-cookie)	2m 26s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-server-required-and-nullable-properties)	2m 0s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-server/javalin)	2m 6s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-server/jaxrs-spec-mutiny)	1m 45s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-server/ktor2)	2m 5s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-server/javalin-6)	2m 5s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-server/ktor)	2m 1s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-misk)	1m 53s
Build Kotlin server (jdk17) (samples/server/petstore/kotlin-server/jaxrs-spec)	1m 33s
	24m 32s

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