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.

tests/acceptance/packs/guardrails/fixtures/at1/input.txt

@@ -0,0 +1 @@
+fixture at1 deterministic stub

tests/acceptance/packs/guardrails/fixtures/at10/input.txt

@@ -0,0 +1 @@
+fixture at10 deterministic stub

tests/acceptance/packs/guardrails/fixtures/at2/input.txt

@@ -0,0 +1 @@
+fixture at2 deterministic stub

tests/acceptance/packs/guardrails/fixtures/at3/input.txt

@@ -0,0 +1 @@
+fixture at3 deterministic stub

tests/acceptance/packs/guardrails/fixtures/at4/input.txt

@@ -0,0 +1 @@
+fixture at4 deterministic stub

tests/acceptance/packs/guardrails/fixtures/at5/input.txt

@@ -0,0 +1 @@
+fixture at5 deterministic stub

tests/acceptance/packs/guardrails/fixtures/at6/input.txt

@@ -0,0 +1 @@
+fixture at6 deterministic stub

tests/acceptance/packs/guardrails/fixtures/at7/input.txt

@@ -0,0 +1 @@
+fixture at7 deterministic stub

tests/acceptance/packs/guardrails/fixtures/at8/input.txt

@@ -0,0 +1 @@
+fixture at8 deterministic stub

tests/acceptance/packs/guardrails/fixtures/at9/input.txt

@@ -0,0 +1 @@
+fixture at9 deterministic stub