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/process/plugin-capability-catalog.json

@@ -0,0 +1,15 @@
+{
+  "version": "0.1.0-stub",
+  "capabilities": [
+    {
+      "id": "scan",
+      "resources": {"cpu": "500m", "memory": "256Mi"},
+      "requires_network": false
+    },
+    {
+      "id": "report",
+      "resources": {"cpu": "200m", "memory": "128Mi"},
+      "requires_network": false
+    }
+  ]
+}