Feat/crypto registry aes gcm siv (#759)

As discussed in ticket #758, this PR adds AES-GCM-SIV as an AEAD variant
to the Cryptography Registry.

Fixes #758

### Details
- Adds standardized AES-GCM-SIV (RFC 8452) as an `ae` variant under the
existing AES family

### Scope
- Registry data only (`schema/cryptography-defs.json`)
- No schema or specification behavior changes

Author: stevespringett

schema/cryptography-defs.json

@@ -353,6 +353,16 @@
           "pattern": "AES[-(128|192|256)][-(GCM|CCM)][-{tagLength}][-{ivLength}]",
           "primitive": "ae"
         },
+        {
+          "standard": [
+            {
+              "name": "RFC8452",
+              "url": "https://doi.org/10.17487/RFC8452"
+            }
+          ],
+          "pattern": "AES[-(128|192|256)]-GCM-SIV[-{tagLength}][-{ivLength}]",
+          "primitive": "ae"
+        },
         {
           "standard": [
             {