fix(BS-16056) Conversion from Integer to Date in contract (#157)

When a JSON attribute value of type number is deserialized by Jackson,
it becomes an Integer and not a Long when it is small enough. However,
in the contract of the tasks and processes, we only support Long and ISO
String as input for a DATE contract input.
This commit adds the support for Integer

Covers [BS-16056](https://bonitasoft.atlassian.net/browse/BS-16056)