Add NTS-enabled indicator for ntp-ctl status

[michielp1807]

ntp-ctl status now shows for each source if that source is NTS-enabled, e.g.:

Sources:
time.tweede.golf:4460/34.147.28.4:123 [NTS] (1): -0.000101±0.000141(±0.008505)s
    poll interval: 128s, missing polls: 1
    root dispersion: 0.000031s, root delay:0.006897s
    NTS cookies: 7/8 available

if NTS is disabled, nothing changes:

Sources:
ntpd-rs.pool.ntp.org:123/185.51.192.62:123 (1): +0.047054±0.079489(±0.006319)s
    poll interval: 16s, missing polls: 0
    root dispersion: 0.000183s, root delay:0.002304s

The Prometheus output has not (yet) been updated to include a NTS flag

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 81.22%. Comparing base (a859104) to head (c1df5e0). Report is 5 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1647 +/- ## ========================================== + Coverage 81.08% 81.22% +0.14% ========================================== Files 64 64 Lines 19708 19664 -44 ========================================== - Hits 15981 15973 -8 + Misses 3727 3691 -36 ```

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