Functionality: When a logged-in user clicks on a 'request' button, add that entry ID to the `preferences` list

[lpatmo]

[lpatmo]

Two tasks:

• [ ] When a logged-in user clicks on a 'request' button, add that entry ID to the preferences list inside the user's entry.
• [ ] Add the entry ID associated with the user to the other entry's requested list.

  "_id": "spx2LvuC7ZjYgexir",
  "userId": "bMnnxiN8QB3w9nAsZ",
  "category": {
    "id": "1",
    "title": "Accountability Partner"
  }, 
   ...
  "preferences": ["Abx2LvuC7ZjYgex1s"], //entries this entry is interested in
  "requesters": ["SCx2Lvua9ZjYgex23"], //entries that want to be matched with this entry
  "createdAt": "2019-04-04T02:05:43.061Z"
}

[angelocordon]

Should also note that user can only submit an entry for a card once (prevent user from clicking request on the same card multiple times and having duplicated values of the user's ID in the preferences column (array)

[lpatmo]

I'm tackling this now!