Print the time to reach default.target in systemd-analyze time (#7383)

Example output (last line is new):
$ systemd-analyze time
Startup finished in 12.879s (firmware) + 36.999s (loader) + 1.313s (kernel) + 22.672s (initrd) + 3min 1.755s (userspace) = 4min 15.619s
graphical.target reached after 1min 39.377s in userspace