fix: users/:id monthly_supporter_badge only gets returned if the user also prefers_monthly_supporter_badge

[kfc35]

As requested in the github issue:

• I checked for where monthly_supporter is being returned, and it seems to be only in the v2 version of users/:id (v1 users endpoints only returns user data stored in ES documents, which doesn’t have the donor fields as far as I could tell in schema/indices/users.js).
• A new attribute monthly_supporter_badge replaces monthly_supporter for the users/:id endpoint, which takes into account whether the user’s prefers_monthly_supporter_badge is true.
• users/me keeps its logic of returning monthly_supporter regardless of prefers_monthly_supporter_badge

I implemented the solution as a separate query to the preferences table, but if the team is concerned and prefers it to be left joined to the original user query, that can be arranged.

Closes #479

[kfc35]

If you’d rather this case return null instead of false, let me know. I originally had it returning null previously