There is a similar request in Waze App Feature Requests: to send and "i'm driving" text
. Check out other request in that forum.
Prompted by your post, I found several apps that automatically respond to calls and texts while driving - it senses movement - configure the speed to be enabled (so not when you are walking or going for a jog) and allows up to 3 apps to be allowed (a nav app like waze, music, etc,)
I just installed this one Safely Go
there are others for Android and IPhone.