MAR-192: Switch to using NTPsec NTP server for increased security:

- This has for some time been a way better option, and it should also
provide for compatibility with Debian 12 Bookworm.

MAR-154: Drop support for Python 2.7 from the common role:

- This primarily concerns removal of pip requirements upgrade checks
for Python 2.7.
- The old Python 3-specific paths are getting deprecated, and the
Python 2 paths will be used instead.
- Set permissions on pipreqcheck directory explicitly (because of
deprecation testing).