Added flag and tests for SubscriptionPlan changes

Adding a flag and supporting tests for changes to SubscriptionPlan to
provide a subscription status and the plan's end date if available.

Flag: com.android.internal.telephony.flags.subscription_plan_allow_status_and_end_date

Test: atest phone FrameworksTelephonyTests:SubscriptionPlanTest
Bug: 357272015
Change-Id: I25b70907eda6b3bcbf34f786ed86d64432c7331f
diff --git a/flags/subscription.aconfig b/flags/subscription.aconfig
index 543aa20..4c00210 100644
--- a/flags/subscription.aconfig
+++ b/flags/subscription.aconfig
@@ -72,3 +72,11 @@
     purpose: PURPOSE_BUGFIX
   }
 }
+
+# OWNER=jmattis TARGET=25Q2
+flag {
+  name: "subscription_plan_allow_status_and_end_date"
+  namespace: "telephony"
+  description: "Provide APIs to retrieve the status and recurrence rule info on a subscription plan"
+  bug: "357272015"
+}