Add MergeUsageAnalyzer to detect legacy merge service usage

- Implemented MergeUsageAnalyzer to flag usage of AdvisoryMergeService and AddMergeModule.
- Created AnalyzerReleases.Shipped.md and AnalyzerReleases.Unshipped.md for release documentation.
- Added tests for MergeUsageAnalyzer to ensure correct diagnostics for various scenarios.
- Updated project files for analyzers and tests to include necessary dependencies and configurations.
- Introduced a sample report structure for scanner output.

src/Scanner/__Tests/StellaOps.Scanner.WebService.Tests/ReportSamplesTests.cs

@@ -28,8 +28,8 @@ public sealed class ReportSamplesTests
         Assert.NotNull(response!.Report);
         Assert.NotNull(response.Dsse);
 
-        var reportBytes = JsonSerializer.SerializeToUtf8Bytes(response.Report, SerializerOptions);
-        var expectedPayload = Convert.ToBase64String(reportBytes);
-        Assert.Equal(expectedPayload, response.Dsse!.Payload);
-    }
+        var reportBytes = JsonSerializer.SerializeToUtf8Bytes(response.Report, SerializerOptions);
+        var expectedPayload = Convert.ToBase64String(reportBytes);
+        Assert.Equal(expectedPayload, response.Dsse!.Payload);
+    }
 }