feat: support printing of datetime without seconds

[olivroy]

It doesn't seem to work for now, but opening for discussion

Addresses #647

Seems to work, but the tests don't work.

[krlmlr]

Thanks. Is this a snapshot test that needs updating?

The "simple" shaft may work here, but should we perhaps use adaptive rendering (https://vctrs.r-lib.org/articles/pillar.html#adaptive-rendering) to support a larger variety of patterns?