feat: report unknowns in sbom (#2998)

Signed-off-by: Keith Zantow <kzantow@gmail.com>
Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>
Co-authored-by: Alex Goodman <wagoodman@users.noreply.github.com>

schema/json/schema-latest.json

@@ -1,6 +1,6 @@
 {
   "$schema": "https://json-schema.org/draft/2020-12/schema",
-  "$id": "anchore.io/schema/syft/json/16.0.17/document",
+  "$id": "anchore.io/schema/syft/json/16.0.18/document",
   "$ref": "#/$defs/Document",
   "$defs": {
     "AlpmDbEntry": {
@@ -777,6 +777,12 @@
         },
         "executable": {
           "$ref": "#/$defs/Executable"
+        },
+        "unknowns": {
+          "items": {
+            "type": "string"
+          },
+          "type": "array"
         }
       },
       "type": "object",