move validation to separate core package, add generation service

some code cleanup

core/build.gradle.kts

@@ -0,0 +1,7 @@
+group = "com.github.dannecron.demo"
+version = "single-version"
+
+dependencies {
+    implementation(rootProject.libs.spring.boot.starter.validation)
+    implementation(rootProject.libs.json.schema.validator)
+}