Create a daily sanity check script

As discussed at weekly sysadm meeting a few weeks ago:

Add "daily sanity check" script on each machine.

Checking for example the following and sending email if problems are found:

• is ansible running every hour as it should? this is done by the XXX task in YYY, should we simply extend that?
• is ansible using some special branch (not main branch)?
• is systemd-networkd used?
• is both ipv4 and ipv6 configured?
• is nftables config as expected?
• are there any unsupported packages installed? See glasklar/services/misc#116 (closed)

The idea is that such a script would run once a day (perhaps during nighttime), not every hour like the already existing ansible check. The daily sanity check should tell us about things that we want to know about but that we do not want to be nagged about as often as every hour. (We could think about if it should run more seldom than once a day, like once a week, maybe.)