FEM Lab: add Simple Dropdown task editor

[lcjohnso]

Expected behavior

I can configure the FEM "Simple Dropdown" task (a simplified version of the PFE Dropdown task, lacking multiple cascading dropdowns or accepting user input) from the FEMLab version of the project builder workflow editor page.

Current behavior

The FEMLab workflow editor page still shows full PFE dropdown task editor, including features that are not implemented in FEM.

Additional information

Relevant Links:

• Simple Dropdown ADR: https://github.com/zooniverse/front-end-monorepo/blob/master/docs/arch/adr-30.md
• Simple Dropdown Implementation PR: Classifier Dropdown Task (v3) - Simple Dropdown front-end-monorepo#1772
• FEM Dropdown Discussion: [RFC] Dropdown Task front-end-monorepo#2428

We may need to take care when deploying this change with regard to potentially affected projects. Example: will NfN still be able to make necessary edits?