user: add a field to indicate whether the password is set

A structure similar to the one used for secrets would be better,
but we don't want to break backwards compatibility.

Also document that omitting the password field in the request body
will preserve the current password when updating a user using the
REST API. Added a test case for this.

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

pkgs/build.sh

@@ -1,6 +1,6 @@
 #!/bin/bash
 
-NFPM_VERSION=2.27.1
+NFPM_VERSION=2.28.0
 NFPM_ARCH=${NFPM_ARCH:-amd64}
 if [ -z ${SFTPGO_VERSION} ]
 then