Add license type: Apache2 is a NOTICE license

Bug: 68860345
Bug: 69058154
Bug: 151953481

Test: no code changes

Change-Id: I5f0eb07980082b8bb11f4c56cdaf7a8dd674105f
diff --git a/METADATA b/METADATA
index 937090d..98a8942 100644
--- a/METADATA
+++ b/METADATA
@@ -10,6 +10,7 @@
     value: "https://github.com/sybrenstuvel/python-rsa/"
   }
   version: "version-4.0"
+  license_type: NOTICE
   last_upgrade_date {
     year: 2019
     month: 2