feat(sdk-android): throwaway sample app for SDK validation

Single-activity Android app that calls Uatu.start() in
SampleApplication.onCreate and registers three extractors
(app_state, click_count, uptime_millis). MainActivity has a
button so click_count exercises non-trivial state.

settings.gradle.kts

@@ -19,3 +19,5 @@ rootProject.name = "uatu"
 include(":sidecar")
 include(":sdk-android")
 project(":sdk-android").projectDir = file("sdk/android")
+include(":sdk-android-sample")
+project(":sdk-android-sample").projectDir = file("sdk/android/sample")