Added Fundraiser to donations

[edwoodward]

API URL: http://localhost:8000/apps/cms/api/donations/fundraiser/?format=json

JSON:

[
  {
    "color_scheme":"red",
    "message_type":"message",
    "headline":"Pay it <span class=\"color\">forward.</span>",
    "message":"Messaging that talks about how OpenStax free resources help students graduate, and how OpenStax relies on charitable contributions.",
    "button_text":"Give today",
    "button_url":"/give",
    "box_headline":"Lorem ipsum dolor sit amet lorem ipsum dolor lorem sit amet.",
    "box_html":"Even donations of just <b>$1, $5, or $10</b> can lorem ipsum dolor sit amet.",
    "fundraiser_image":"http://localhost:8000/media/sample-blue-200x200.jpg",
    "goal_amount":1234,
    "goal_time":"2022-01-12T09:07:01-06:00"
  }
]

Added API to wiki