Deprecate Jackson 2 support for execution context serialization

Related to #4842

Author: fmbenhassine

spring-batch-core/src/main/java/org/springframework/batch/core/repository/dao/Jackson2ExecutionContextStringSerializer.java

@@ -108,7 +108,10 @@
  * @author Mahmoud Ben Hassine
  * @since 3.0.7
  * @see ExecutionContextSerializer
+ * @deprecated Since 6.0 in favor of {@link JacksonExecutionContextStringSerializer}.
+ * Scheduled for removal in 7.0.
  */
+@Deprecated(since = "6.0", forRemoval = true)
 @NullUnmarked
 public class Jackson2ExecutionContextStringSerializer implements ExecutionContextSerializer {