Specifies the priority of this app release for the in-app update feature
of the Google Play Core Library.
If you don't use this feature, or don't need to set a priority, you can leave
this field blank; it will default to 0. Otherwise the value must be a whole
number between 0 (lowest priority) and 5 (highest priority).
For more information on using in-app updates, see the documentation:
https://developer.android.com/guide/playcore/in-app-updates
This field supports substituting environment variables in the form
${SOME_VARIABLE} or $SOME_VARIABLE at build time.