The field `avatar` type is mixed: | Attribute | Type | Description | | ------ | ------ |------ | | avatar | mixed |Image file for avatar of the project| But doesn't specify the format of the file, `base64`, `FileBlob`, `url` ? I Always get 400 Bad request, avatar field is invalid. We should add an example cURL request in `doc/api/projects.md`. <!-- Don't edit below this line -->