Add subscriber to Board

Request

• Base URL
  /v1 (relative, and the document was published on a file host, not at the API’s origin)
• Auth
  none declared
• TypeScript
  https://skmtc.dev/restyaplatform/apis/restyaboard/docs/v1/boards/:boardId/board_subscribers.json/post.ts

  A function with typed inputs. Its response is checked against the schema.