CIP-0010 | Add label: On-chain certification metadata (#500)

* Update registry.json: Certification metdata

Added transaction_metadatum_label 1304 to registry.json for the Certification metadata from CIP-0123

* no CIP number for this metadata standard yet

---------

Co-authored-by: Robert Phair <rphair@cosd.com>

CIP-0010/registry.json

@@ -55,6 +55,10 @@
     "transaction_metadatum_label": 1226,
     "description": "Oracle related transaction metadata"
   },
+  {
+    "transaction_metadatum_label": 1304,
+    "description": "on-chain certification metadata"
+  },
   {
     "transaction_metadatum_label": 1564,
     "description": "Marlowe - a DSL for writing and executing financial contracts"