136 use kotlinx instant in auditable

[pavliuc75]

changed auditable to use kotlinx.datetime.Instant
#136

[pavliuc75]

the problem was that the converter would only work with the existing records from db.
the converter works for javainstant<->kotlininstant
when a new db record is created, spring uses java.time.localdatetime by default
since we only have a converter between javainstant<->kotlininstant and not localdatetime, this is what was causing the problem.
the solution is changing the default spring configuration to use javainstant for auditing

[yuanchen233]

When go in Deployments in the portal,

10:47:29.749 [http-nio-8080-exec-2] INFO  d.c.c.w.s.controller.StudyController - Start GET: /api/studies/ca4f7ecf-6b74-4c58-b4b4-f5e4a81ad514/participantGroup/status
10:47:30.026 [http-nio-8080-exec-9] ERROR d.c.c.w.c.e.advices.ExceptionAdvices - Uncaught Exception: CarpErrorResponse(statusCode=500, exception=java.lang.ClassCastException, message=class kotlinx.datetime.Instant cannot be cast to class java.time.Instant (kotlinx.datetime.Instant is in unnamed module of loader 'app'; java.time.Instant is in module java.base of loader 'bootstrap'), path=GET /api/studies/ca4f7ecf-6b74-4c58-b4b4-f5e4a81ad514/participantGroup/status)
10:47:30.028 [http-nio-8080-exec-9] WARN  o.s.w.s.m.m.a.ExceptionHandlerExceptionResolver - Resolved [java.lang.ClassCastException: class kotlinx.datetime.Instant cannot be cast to class java.time.Instant (kotlinx.datetime.Instant is in unnamed module of loader 'app'; java.time.Instant is in module java.base of loader 'bootstrap')]