(#19542) useradd provider should support move-home option if managehome is enabled

usermod has a flag (-m) to move a users home directory when it's being modified, this
adds modifycmd to the useradd provider which will run usermod with the -m option.
(#19542) Update user type docs for linux managehome

Commit d23906e adds support for updating the user home directory if the
`managehome` parameter is true. This commit updates the user type
documentation to note the Linux exception since the behavior change is
only applicable to Linux.
Merge branch 'pull-1512'