Document how to select/override maplibre dependency on android

[sargunv]

MapLibre will initially have vulkan as a separate package: maplibre/maplibre-native#3079

We should figure out what we need to do for a consumer to use that instead of opengl. Is it possible for them to override the dependency we declare in Gradle? If so, document it.

Alternative, maybe we compileOnly against MapLibre on Android and have the consumer provide the chosen dependency explicitly, like we do by necessity for iOS.

[sargunv]

#110