Add MongoDB storage library and update acceptance tests with deterministic stubs

- Created StellaOps.Notify.Storage.Mongo project with initial configuration.
- Added expected output files for acceptance tests (at1.txt to at10.txt).
- Added fixture input files for acceptance tests (at1 to at10).
- Created input and signature files for test cases fc1 to fc5.

docs/scripts/sbom-vex/vex.json

@@ -0,0 +1,11 @@
+{
+  "@context": "https://openvex.dev/ns/v0.2.0",
+  "statements": [
+    {
+      "vulnerability": "CVE-2025-0001",
+      "products": ["pkg:container/example@1.0.0"],
+      "status": "not_affected",
+      "justification": "vulnerable_code_not_present"
+    }
+  ]
+}