camera_metadata: add non-full hw level optional tag

Bug: 10838063
Change-Id: If6d1ef5bd58aca3a9a722e4317f5ce6804dd6680
diff --git a/camera/docs/metadata_parser_xml.py b/camera/docs/metadata_parser_xml.py
index f0ed12e..ec6957f 100755
--- a/camera/docs/metadata_parser_xml.py
+++ b/camera/docs/metadata_parser_xml.py
@@ -158,6 +158,11 @@
     d['visibility'] = entry.get('visibility')
 
     #
+    # Optional for non-full hardware level devices
+    #
+    d['optional'] = entry.get('optional') == 'true'
+
+    #
     # Typedef
     #
     d['type_name'] = entry.get('typedef')