[java] Intro openApiNullable property to enable/disable OpenAPI Jackson Nullable library (#6154)

* Add option to prevent usage of jackson-nullable (#2901)

Add a option for all java client and server to prevent
usage of third party library (jackson-databind-nullable)
which may be forbidden in some company

Add samples for Vertx, Spring MVC, Spring Cloud, Feign and Play

Upgrade dependencies for org.openapitools:jackson-databind-nullable

* Samples - Remove dependency org.openapitools:jackson-databind-nullable (#2901)

* Fix generation of gradle file for vertx (#2901)

* Regenerate samples (#2901)

* Fix documentation and up to date (#2901)

* Fix forgotten regeneration of vertx after dependency integration (#2901)

* Regenerate template after rebase (#2901)

* Use yaml config files introduce in #6509 to manage samples (#2901)

* Regenerate template using the config (#2901)

* Fix bad version during testing generated samples (#2901)

* Regenerate template after fix bad version (#2901)

* Fix merge, allow for set importing on codegen model

Co-authored-by: Jim Schubert <james.schubert@gmail.com>

samples/server/petstore/java-play-framework-no-nullable/build.sbt

@@ -0,0 +1,11 @@
+name := """openapi-java-playframework"""
+
+version := "1.0-SNAPSHOT"
+
+lazy val root = (project in file(".")).enablePlugins(PlayJava)
+
+scalaVersion := "2.12.6"
+
+libraryDependencies += "org.webjars" % "swagger-ui" % "3.23.5"
+libraryDependencies += "javax.validation" % "validation-api" % "1.1.0.Final"
+libraryDependencies += guice