dateTime with clearInput option

[ionitron-bot]

Original issue by @ashgibson on 2018-02-01T03:38:41Z

Ionic version: (check one with "x")
(For Ionic 1.x issues, please use https://github.com/ionic-team/ionic-v1)
[ ] 2.x
[ ] 3.x
[ x] 4.x

I'm submitting a ... (check one with "x")
[ ] bug report
[ x] feature request

Would it be possible to add the clearInput attribute directive on the ion-datetime component so that it is easy for the user to clear the input?