Clarify when to use `date` vs `datetime`

[SmilyOrg]

Adjust rule 169 to consider the following points (up for discussion)

• date should be used for cases where the day itself matters, e.g. holidays, document dates, ETAs (shipping notices), birthdays. Usually this means the "local day", i.e. the time period midnight to midnight in the local time zone.
• datetime should be used to indicate instants/moments in time, i.e. a form was submitted at 2024-02-16T16:19:00Z, it may also be better to implement filtering by dates (e.g. with date picker) as datetime to make the client decide on whether a date is implicit or explicit and which timezone it refers to (unless the filtering would filter to events that happened on a certain day in every timezone,)

[ePaul]

We agreed it should be a new rule, not part of 169. Working title:

• Should select appropriate one of date or date-time format

(Internal discussion notes)

[ePaul]

Done with #808.