Changes to allow user-specific umask in the server settings.

[scottfridwin]

This adds a new configuration setting that allows setting a specific umask value for each user. The umask is a string variable, but it should be a valid umask value. The config looks like this:

"Users": [
        {
            "Username": "user1",
            "Password": "pass1",
            "UID": 1001,
            "GID": 1003,
            "Chroot": {
                "Directory": "/user",
                "StartPath": "drop"
            }
        },
        {
            "Username": "user2",
            "Password": "pass2",
            "UID": 1002,
            "GID": 1016,
            "Chroot": {
                "Directory": "/user",
                "StartPath": "drop"
            },
            "Umask": "002"
        }
    ]

and it generates this in the sshd_config file:

Match User "user2"
X11Forwarding no
AllowTcpForwarding no
ForceCommand internal-sftp -u 002

Tested it on a custom image and it allowed me to upload files with -rw-rw-r-- permissions instead of default -rw-r--r-- permissions.