[Feature]: Add new volunteer photos / randomness to school profiles

[mattgianni]

Replace the current set of stock photos on the school profile page with a more elaborate system.

Kira created and organized several collections of images in a Google Drive - https://drive.google.com/drive/folders/1NJ5DigzdrgV1PjXmJTYPelsp_ZfhoZkP. The images are organized into categories based on grade level (HS, MS, K-5) and type (Mentor, Event, Tutor, Other).

Each school profile page should present an appropriate image based on these categories. These images should be randomly distributed across the schools, but the same school should always use the same randomly assign set. (suggestion, use a hash of the school name or other durable identifier to select the images).