Add activity label to encryption interstitial

So that TalkBack refers to the screen by this more specific name.

Bug: 28868846
Change-Id: I93139959dcdbd156d57f01699283e01b178305b8
diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index 6ba161e..d5fe301 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -1732,6 +1732,7 @@
             android:windowSoftInputMode="stateVisible|adjustResize"/>
 
         <activity android:name=".SetupEncryptionInterstitial"
+            android:label="@string/encryption_interstitial_header"
             android:taskAffinity="com.android.wizard"
             android:theme="@style/SetupWizardDisableAppStartingTheme"/>