Add "Relationship" dropdown to triplee entry

[shauminn-colab]

As an ambassador, I want to specify a Triplee's relationship to the Tripler when they are not housemates.

Backend task that is dependent upon this: colab-coop/HelloVoter#41

• On /triplers/confirm/ page where Triplee info is added for 3 Triplees ("Voters" in the product), when the Housemate checkbox is unchecked (which is the default state), display a "Relationship" dropdown next to the Housemate checkbox with the following items:
  Parent
  Sibling
  Other family
  Neighbor
  Friend
• Update JSON for triplees to include the Relationship selection
• Add new frontend env var SHOW_TRIPLEE_RELATIONSHIP_DROPDOWN so that we can configure whether Relationship dropdown is visible per organization - the 2 configurable states would be true if visible and empty if not visible. The items in the dropdown itself wouldn't be configurable

Backend task that is dependent upon this: colab-coop/HelloVoter#41

Current page layout for reference: