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/proof-manifest.json

@@ -0,0 +1,11 @@
+{
+  "version": "0.1.0-stub",
+  "chain_hash": "7d72ed74065e8e359af34c5bb1805fa62629e2444dbe77b89efbebe5c4ddb932",
+  "inputs": {
+    "sbom": "sbom.json",
+    "vex": "vex.json",
+    "dsse": "envelope.dsse",
+    "rekor_bundle": "rekor-bundle.json"
+  },
+  "lockfile": "inputs.lock"
+}