Reconsider date and time picker component

[mmenestr]

In the following issue, we discussed whether the current date and time picker implementation is really the best way to go forward: patternfly/patternfly-react#8868

Issue
The current implementation combines the date and time in the same toggle, but separates the selection menus. I think it would make more sense to have one menu, to match the fact that the date and time are in the same toggle.

Additionally, due to implementation reasons, the toggles to open those menus do not use the same styles around the icon which looks weird (one uses the classic input group styling, while the other uses a dropdown styling).

Proposal
We either:

1. Create a new component similar to the "Calendar month" component that includes both the ability to select a date AND a time within the same men
   OR
2. Get rid of this combined "Date and time picker" component, and update our guidance to say that if both a date and time picker are needed in a design, they should be placed side by side as two separate components.

cc: @mcarrano