Set minSdk explicitly in AndroidManifest.xml

This allows merging manifests for LOCAL_STATIC_ANDROID_LIBRARIES. This should
practically be a no-op.

Test: m -j
Change-Id: I26267dd3f263328955fe7ffb46697ad8dae12d5a
Bug: 78447299
diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index e413156..6d2675b 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -22,6 +22,8 @@
     <uses-permission android:name="android.permission.READ_CONTACTS" />
     <uses-permission android:name="android.permission.MANAGE_USERS" />
 
+    <uses-sdk android:minSdkVersion="21"/>
+
     <application
         android:defaultToDeviceProtectedStorage="true"
         android:icon="@mipmap/ic_local_hospital_24dp"