[Reference][Form Types] Document "with_minutes" time/datetime option

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | yes
| Applies to    | 2.3+
| Fixed tickets | #3410 (task `time > with_minutes`)

The `datetime` field also has a `with_minutes` option.

Using the `single_text` widget type might not work as expected using `with_minutes=false` if the browser supports HTML5's `time` input type. Most browsers seem to only support `hh:mm` or `hh:mm:ss` formats for the value attribute (resetting the value to `--:--` if using an hour value only). This might not be the case for every browser because I couldn't find anything in the HTML5 spec that says a partial time cannot be an hour only. I've added a `caution` box for this.