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.

.gitignore

@@ -14,11 +14,11 @@ obj/
 .idea/
 .vscode/
 
-# Packages and logs
-*.log
-TestResults/
-local-nuget/
-local-nugets/packages/
+# Packages and logs
+*.log
+TestResults/
+local-nuget/
+local-nugets/packages/
 
 .dotnet
 .DS_Store
@@ -31,11 +31,32 @@ seed-data/cert-bund/**/*.sha256
 out/offline-kit/web/**/*
 **/node_modules/**/*
 **/.angular/**/*
-**/.cache/**/*
-**/dist/**/*
-tmp/**/*
-build/
-/out/cli/**
-/src/Sdk/StellaOps.Sdk.Release/out/**
-/src/Sdk/StellaOps.Sdk.Generator/out/**
-/out/scanner-analyzers/**
+**/.cache/**/*
+**/dist/**/*
+tmp/**/*
+build/
+/out/cli/**
+/src/Sdk/StellaOps.Sdk.Release/out/**
+/src/Sdk/StellaOps.Sdk.Generator/out/**
+/out/scanner-analyzers/**
+
+# Node / frontend
+node_modules/
+dist/
+.build/
+.cache/
+
+# .NET
+bin/
+obj/
+
+# IDEs
+.vscode/
+.idea/
+*.user
+*.suo
+
+# Misc
+logs/
+tmp/
+coverage/