* implement UI for the formula field

* consider utilizing the components for generated work package subjects

* [pattern input](https://github.com/opf/openproject/blob/dev/app/components/work_packages/types/pattern_input.rb)

* [pattern input controller](https://github.com/opf/openproject/blob/dev/frontend/src/stimulus/controllers/pattern-input.controller.ts)

* offer dropdown containing

* mathematical operators and parenthesis

* custom fields of type integer and float

* custom fields of type calculated value Begin of the deletion

* consider custom fields when validating the formula

* perform the calculation for the given formula

* basic error handling

* is any of the referenced custom fields deactivated/missing?

* is there a mathematical error?

* **open point:** define data structure for saving the formula to the DB. JSONB?End of the deletion