2.0 dev threatmodeling staging (#951)

A series of enhancements, corrections, and minor refactors of some of
the schemas supporting threat modeling.

Author: stevespringett

schema/2.0/cyclonedx-2.0.schema.json

@@ -64,6 +64,12 @@
     "vulnerabilities": {
       "$ref": "model/cyclonedx-vulnerability-2.0.schema.json#/$defs/vulnerabilities"
     },
+    "threats": {
+      "$ref": "model/cyclonedx-threat-2.0.schema.json#/$defs/threats"
+    },
+    "risks": {
+      "$ref": "model/cyclonedx-risk-2.0.schema.json#/$defs/risks"
+    },
     "annotations": {
       "$ref": "model/cyclonedx-annotation-2.0.schema.json#/$defs/annotations"
     },