dev.knotless.uploadAvatar

Uploads the body, a PNG, JPEG, WebP or GIF, as a blob of the account logged in to this appview's web pages, and names it as the picture of its dev.knotless.profile record, as `knotless account profile --avatar` does: one that is not a PNG or JPEG, or is over 1,000,000 bytes, is drawn again as a JPEG that fits, at most 2000 pixels on its longest side. Requires the session cookie the pages' login sets: the appview writes with the session it keeps for that account.