[cpesuggest] Add CPE security tag for httplib2.

I have manually checked the CPE tag is correct by checking the vendor
and product name match on the NVD site (version # does not need to
match).
https://nvd.nist.gov/products/cpe/search/results?namingFormat=2.2&keyword=cpe:/a:httplib2_project:httplib2&status=FINAL%2CDEPRECATED

Adding CPE security tags to a METADATA file is necessary to
enable automated vulnerability monitoring.

Bug: 396670837

Change-Id: Ib1974b23530aea4ce13cdb570cbb3b0406bf5ab1

METADATA

diff --git a/METADATA b/METADATA
index 9b4842c..7d702f5 100644
--- a/METADATA
+++ b/METADATA
@@ -10,8 +10,11 @@
     value: "https://github.com/httplib2/httplib2.git"
   }
   version: "v0.18.1"
-  license_note: "would be NOTICE save for: test/other_cacerts.txt and doc/html/_static/jquery.js"
   license_type: RESTRICTED
+  license_note: "would be NOTICE save for: test/other_cacerts.txt and doc/html/_static/jquery.js"
+  security {
+    tag: "NVD-CPE2.3:cpe:/a:httplib2_project:httplib2:0.18.1"
+  }
   last_upgrade_date {
     year: 2020
     month: 5