plugin XEP-0363, upload: File upload (through HTTP upload only for now): - HTTP upload implementation - if the upload link is HTTPS, certificate is checked (can be disabled on demand) - file can be uploaded directly, or a put/get slot can be requested without actual upload. The later is mainly useful for distant frontends like Libervia - upload plugin manage different upload methods, in a similar way as file plugin - download url is sent in progressFinished metadata on successful upload