fix(android): enable BuildConfig generation

[gulsher7]

While upgrading our React Native app from 0.86.3 to 0.87.1, we started getting the following error from the AppsFlyer Android module:

defaultConfig contains custom BuildConfig fields, but the feature is disabled.

The issue is caused by INCLUDE_CONNECTOR being defined using buildConfigField, while BuildConfig generation is disabled with the newer Android Gradle Plugin version.

This change enables BuildConfig generation for the AppsFlyer Android library:

buildFeatures {
    buildConfig = true
}