feat(registry): add AES-SIV AEAD variant (RFC 5297) (CycloneDX#764)

As discussed in ticket CycloneDX#763, this PR adds AES-SIV (RFC 5297) as an AEAD
variant to the Cryptography Registry.

Fixes CycloneDX#763

Details
- Adds `AES[-(128|192|256)]-SIV` as an `ae` variant under the existing
`AES` family.
- Adds authoritative standards reference for RFC 5297.
- Registry-only change (`schema/cryptography-defs.json`). No schema or
specification behavior changes.

Author: stevespringett

schema/cryptography-defs.json

@@ -363,6 +363,16 @@
           "pattern": "AES[-(128|192|256)]-CTR-HMAC-SHA1[-96]",
           "primitive": "ae"
         },
+        {
+          "standard": [
+            {
+              "name": "RFC 5297",
+              "url": "https://doi.org/10.17487/RFC5297"
+            }
+          ],
+          "pattern": "AES[-(128|192|256)]-SIV",
+          "primitive": "ae"
+        },
         {
           "standard": [
             {