Add support for OffsetDateTime and OffsetTime

[cromoteca]

Describe your motivation

The generator supports the java.time.Local* date types, but not the Offset* counterparts. This is unfortunate, as they are the preferred classes for data transfer. From the java.time JavaDoc:

The offset-based date-time types OffsetTime and OffsetDateTime, are intended primarily for use with network protocols and database access.

Describe the solution you'd like

Those types are mapped to string instead of unknown.

Describe alternatives you've considered

There are easy workarounds like casting on the client or using a DTO that converts to String, but they are quite ugly.

Additional context

There's a related forum thread from @deniz-frick that illustrates the issue.

[platosha]

Note that we need to update the CRUD components to support OffsetTime/OffsetDateTime.