Add a warning to lunch command for metrics collection

When metrics collection is enabled but
there's no gcert, print a warning and ask the user to run gcert so that
metrics collection can work.

Bug: b/184040091
Change-Id: Ib79c61e89a42dc7da9ef452b7101dac955859a7d

envsetup.sh

@@ -719,6 +719,10 @@ function lunch()
     set_stuff_for_environment
     [[ -n "${ANDROID_QUIET_BUILD:-}" ]] || printconfig
     destroy_build_var_cache
+
+    if [[ -n "${CHECK_MU_CONFIG:-}" ]]; then
+      check_mu_config
+    fi
 }
 
 unset COMMON_LUNCH_CHOICES_CACHE