Tasks with images or files

[OlegZapara]

Usually tasks require images or files that cannot be used with via url. To solve this problem we need to add a possibility to attach them to task

Telegram: after task is created user can reply to bot message with an image or a file, which will then be used for it . Only first reply is accepted, rest is ignored. /due command also gives multiple messages - task image or file and task (if there is one) and task description.
Website: add endpoints for uploading and deleting an image of the task if task already exists. Update existing endpoints to match new functionality

Another way to implement this functionality is to not store images or files on the server, rather just to store message ID that was replied to task. /due will reply with task description to each of the task attachments
Web version would not work in such way, since there were no reply message