[wip] Avatars

Still a work in progress.

Status:

- [x] `GET /v1/avatar`
- [x] `GET /v1/avatars`
- [x] `POST /v1/avatar`
- [x] `POST /v1/avatar/upload`
- [ ] store images on s3 private bucket
- [x] image processing worker to resize images
- [ ] put processed images on s3 public bucket
- [ ] domain and proxy for s3 public bucket