Updates case contact form to use dropdown selector

[kenny-luong]

What github issue is this PR for, if any?

Resolves #5776

What changed, and why?

1. Picker updated to dropdown selector
2. Names of the assigned volunteers are displayed next to the case ids only for supervisors
3. Updated various supporting code for specs to use the new dropdown selector

How is this tested? (please write tests!) 💖💪

I updated the specs to use the new dropdown

Screenshots please :)

http://localhost:3000/case_contacts/64/form/details

[schoork]

Commenting for my visibility