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/expected/at1.txt

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

tests/acceptance/packs/guardrails/expected/at10.txt

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

tests/acceptance/packs/guardrails/expected/at2.txt

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

tests/acceptance/packs/guardrails/expected/at3.txt

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

tests/acceptance/packs/guardrails/expected/at4.txt

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

tests/acceptance/packs/guardrails/expected/at5.txt

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

tests/acceptance/packs/guardrails/expected/at6.txt

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

tests/acceptance/packs/guardrails/expected/at7.txt

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+expected at7 deterministic stub

tests/acceptance/packs/guardrails/expected/at8.txt

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

tests/acceptance/packs/guardrails/expected/at9.txt

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