`DateTime` documentation improvements

[ruheni]

### Tasks
- [ ] https://github.com/prisma/docs/issues/668
- [ ] https://github.com/prisma/docs/issues/3861
- [ ] https://github.com/prisma/docs/issues/3157
- [ ] https://github.com/prisma/docs/issues/812
- [ ] https://github.com/prisma/docs/issues/548
- [ ] https://github.com/prisma/docs/issues/2755

[jharrell]

Closing this as we're tracking in the sub issues.