Change Telecom Excecutor to cached thread pool

This may help with perf issues (ex: CTS ) as more
modules within Telecom use this executor which is
passed into to them by TelecomSystem

(see example CTS bug on AVD https://b.corp.google.com/issues/276283203#comment5)

Fixes: 276966319
Change-Id: Id1ac319f8d8911d87fb1da7506ed0bd0b090f3a1
Test: telecom cts
diff --git a/src/com/android/server/telecom/components/TelecomService.java b/src/com/android/server/telecom/components/TelecomService.java
index efa9417..ef85fc7 100644
--- a/src/com/android/server/telecom/components/TelecomService.java
+++ b/src/com/android/server/telecom/components/TelecomService.java
@@ -214,7 +214,7 @@
                                             .stopFlashNotificationSequence(context);
                                 }
                             },
-                            Executors.newSingleThreadExecutor(),
+                            Executors.newCachedThreadPool(),
                             new BlockedNumbersAdapter() {
                                 @Override
                                 public boolean shouldShowEmergencyCallNotification(Context