Implement ledger metrics for observability and add tests for Ruby packages endpoints

- Added `LedgerMetrics` class to record write latency and total events for ledger operations.
- Created comprehensive tests for Ruby packages endpoints, covering scenarios for missing inventory, successful retrieval, and identifier handling.
- Introduced `TestSurfaceSecretsScope` for managing environment variables during tests.
- Developed `ProvenanceMongoExtensions` for attaching DSSE provenance and trust information to event documents.
- Implemented `EventProvenanceWriter` and `EventWriter` classes for managing event provenance in MongoDB.
- Established MongoDB indexes for efficient querying of events based on provenance and trust.
- Added models and JSON parsing logic for DSSE provenance and trust information.

src/Excititor/StellaOps.Excititor.WebService/Extensions/TelemetryExtensions.cs

@@ -7,6 +7,7 @@ using OpenTelemetry.Metrics;
 using OpenTelemetry.Resources;
 using OpenTelemetry.Trace;
 using StellaOps.Excititor.WebService.Options;
+using StellaOps.Excititor.WebService.Telemetry;
 using StellaOps.Ingestion.Telemetry;
 
 namespace StellaOps.Excititor.WebService.Extensions;
@@ -64,6 +65,7 @@ internal static class TelemetryExtensions
             {
                 metrics
                     .AddMeter(IngestionTelemetry.MeterName)
+                    .AddMeter(EvidenceTelemetry.MeterName)
                     .AddAspNetCoreInstrumentation()
                     .AddHttpClientInstrumentation()
                     .AddRuntimeInstrumentation();