[UX] Add Multi-Select Dropdown Question Type to Application Form

[ori-near]

Background

Right now, when an admin adds a "Select" (dropdown) question to an application form, the applicant can only pick one answer.

This is a problem for questions where the answer should clearly be multiple things. For example, if we ask: "What areas does your project contribute to? (e.g. wallets, bridges, tools)," the applicant might need to pick all three, but they can't. This makes the data we collect incomplete or wrong. Or forces admin to use a text area question type.

We need a new question type that lets people select as many options as they need from a list.

Scope

This ticket is for figuring out the UX:

1. Admins: Show what it looks like for an admin to choose, name, and set up the options for the new "Multi-Select" question in the form editor.
2. Show the user experience for talent when they fill out the form (how they open the list, select multiple items, and see what they've chosen).
3. Once the design is approved, create a follow up ticket for implementation