Implement Advisory Canonicalization and Backfill Migration

- Added AdvisoryCanonicalizer for canonicalizing advisory identifiers.
- Created EnsureAdvisoryCanonicalKeyBackfillMigration to populate advisory_key and links in advisory_raw documents.
- Introduced FileSurfaceManifestStore for managing surface manifests with file system backing.
- Developed ISurfaceManifestReader and ISurfaceManifestWriter interfaces for reading and writing manifests.
- Implemented SurfaceManifestPathBuilder for constructing paths and URIs for surface manifests.
- Added tests for FileSurfaceManifestStore to ensure correct functionality and deterministic behavior.
- Updated documentation for new features and migration steps.

src/Concelier/__Libraries/StellaOps.Concelier.Storage.Mongo/ServiceCollectionExtensions.cs

@@ -108,6 +108,7 @@ public static class ServiceCollectionExtensions
         services.AddSingleton<IMongoMigration, EnsureGridFsExpiryIndexesMigration>();
         services.AddSingleton<IMongoMigration, EnsureAdvisoryRawIdempotencyIndexMigration>();
         services.AddSingleton<IMongoMigration, EnsureAdvisorySupersedesBackfillMigration>();
+        services.AddSingleton<IMongoMigration, EnsureAdvisoryCanonicalKeyBackfillMigration>();
         services.AddSingleton<IMongoMigration, EnsureAdvisoryRawValidatorMigration>();
         services.AddSingleton<IMongoMigration, EnsureAdvisoryObservationsRawLinksetMigration>();
         services.AddSingleton<IMongoMigration, EnsureAdvisoryEventCollectionsMigration>();