Extend the Expression form component to compute variables when form is loaded / initiated

[volodymyr-melnykc]

Is your feature request related to a problem? Please describe.

Currently, if the user needs to have variables available in a form, they should be defined outside the form, e.g. in the BPMN process.
We can let users use the Expression form component to define initial form variables.
As of the 8.5 release, the Expression form component can compute variables when form values (used in the expression) change or when a form is submitted. It can be extended to make computations happen at form load/initiation time.
In this case, the user doesn’t have to go to the process to define variables that are needed only inside the form.

Describe the solution you'd like

Extend the Expression form component to compute variables when a form is loaded/initiated.

Describe alternatives you've considered

A holistic data management solution for forms.

Additional context

[volodymyr-melnykc]

@Skaiir let's discuss this together.