Determine a suitable default value for minSdkVersion

The minSdkVersion is currently set to 17 (Android-4 2012).

When building the app with a common plugin like @nativescript/background-http the build will fail.

Execution failed for task ':app:processDebugMainManifest'.
Manifest merger failed : uses-sdk:minSdkVersion 17 cannot be smaller than version 21 declared in library [net.gotev:uploadservice:4.7.0] /Users/ianbrindley/.gradle/caches/transforms-3/24fa1312ea1be6efbab27240facdcfb1/transformed/jetified-uploadservice-4.7.0/AndroidManifest.xml as the library might be using APIs not available in 17
        Suggestion: use a compatible library with a minSdk of at most 17,
                or increase this project's minSdk version to at least 21,
                or use tools:overrideLibrary="net.gotev.uploadservice" to force usage (may lead to runtime failures)

Instead I have to add additional configuration to gradle to get this plugin to work.

I suggest that the minSdkVersion is set to 21.

Start from the Android build configuration that defines the default minSdkVersion and reproduce the manifest-merger failure with @nativescript/background-http. Check the compatibility implications of changing the default from 17 to 21, then verify that the plugin builds without extra Gradle configuration. Done means the project uses the agreed default and the reported build succeeds.