On 7th May, 2019 androidx.lifecycle:*:2.2.0-alpha01 was released announcing:
androidx.lifecycle:*:2.2.0-alpha01
This release adds new features that adds support for Kotlin coro
I actually spent a couple hours trying to figure this out myself and it turns out it is in a new package that only exists as of the alpha. Add this and you should be good to go.
implementation "androidx.lifecycle:lifecycle-runtime-ktx:$lifecycle_ver"