MR2 Telemetry: Opening screen preference (#22333)

* For #22145 - Added telemetry to the opening screen preference.

* For #22145 - Added PR number to metric

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

app/metrics.yaml

@@ -1381,6 +1381,22 @@ customize_home:
     notification_emails:
       - android-probes@mozilla.com
     expires: "2022-09-20"
+  opening_screen:
+    type: string
+    description: |
+      What opening screen preference the user has selected
+      under "Customize Home".
+      "homepage," "last tab," or "homepage after 4 hours"
+      default: "homepage after 4 hours"
+    bugs:
+      - https://github.com/mozilla-mobile/fenix/issues/22145
+    data_reviews:
+      - https://github.com/mozilla-mobile/fenix/pull/22333
+    data_sensitivity:
+      - interaction
+    notification_emails:
+      - android-probes@mozilla.com
+    expires: "2022-11-01"
 
 preferences:
   studies_enabled:

app/src/main/java/org/mozilla/fenix/FenixApplication.kt

@@ -726,6 +726,14 @@ open class FenixApplication : LocaleAwareApplication(), Provider {
 
     @VisibleForTesting
     internal fun reportHomeScreenMetrics(settings: Settings) {
+        CustomizeHome.openingScreen.set(
+            when {
+                settings.alwaysOpenTheHomepageWhenOpeningTheApp -> "homepage"
+                settings.alwaysOpenTheLastTabWhenOpeningTheApp -> "last tab"
+                settings.openHomepageAfterFourHoursOfInactivity -> "homepage after four hours"
+                else -> ""
+            }
+        )
         components.analytics.experiments.register(object : NimbusInterface.Observer {
             override fun onUpdatesApplied(updated: List<EnrolledExperiment>) {
                 CustomizeHome.jumpBackIn.set(settings.showRecentTabsFeature)