Valtimo backend libraries (9.23.0)

New Features

The following features were added:

Allow external fields to have a nested formfield.key structure
Previously an external field definition only supported 1 level keys like:
- ex.keyName
Now its possible to define nested stuctures like:
- ex.keyName.anotherKeyName Resulting in structures that can be mapped into the prefilling/submission phase:
```
{
    "ex" : {
        "keyName" : {
             "anotherKeyName" : "someValue"
        }
    }
}
```
Case assignee
It is now possible to assign and unassign a user to a case.
For more information on using this feature see this page.
Information about the endpoints can be found here.

The following bugs were fixed:

Form flow incompatible with PostgreSQL
The Form flow module was failed when loading form flows from the configuration files when using the PostgreSQL DBMS. This has now been resolved.

This version has the following known issues:

Form flow definition does not read nextStep property
- Discovered in version 9.19.0
- Instead of using nextStep, nextSteps can be used.