Add OpenAPI specification for Link-Not-Merge Policy APIs

- Introduced a new OpenAPI YAML file for the StellaOps Concelier service.
- Defined endpoints for listing linksets, retrieving linksets by advisory ID, and searching linksets.
- Included detailed parameter specifications and response schemas for each endpoint.
- Established components for reusable parameters and schemas, enhancing API documentation clarity.

src/Provenance/StellaOps.Provenance.Attestation.Tool/StellaOps.Provenance.Attestation.Tool.csproj

@@ -4,6 +4,7 @@
     <LangVersion>preview</LangVersion>
     <Nullable>enable</Nullable>
     <ImplicitUsings>enable</ImplicitUsings>
+    <OutputType>Exe</OutputType>
     <PackAsTool>true</PackAsTool>
     <ToolCommandName>stella-forensic-verify</ToolCommandName>
     <PackageOutputPath>../../out/tools</PackageOutputPath>

src/Provenance/StellaOps.Provenance.Attestation/Verification.cs

@@ -60,7 +60,7 @@ public static class MerkleRootVerifier
     {
         var provider = timeProvider ?? TimeProvider.System;
         if (leaves is null) throw new ArgumentNullException(nameof(leaves));
-        expectedRoot ??= throw new ArgumentNullException(nameof(expectedRoot));
+        if (expectedRoot is null) throw new ArgumentNullException(nameof(expectedRoot));
 
         var leafList = leaves.ToList();
         var computed = MerkleTree.ComputeRoot(leafList);
@@ -79,7 +79,7 @@ public static class ChainOfCustodyVerifier
     {
         var provider = timeProvider ?? TimeProvider.System;
         if (hops is null) throw new ArgumentNullException(nameof(hops));
-        expectedHead ??= throw new ArgumentNullException(nameof(expectedHead));
+        if (expectedHead is null) throw new ArgumentNullException(nameof(expectedHead));
 
         var list = hops.ToList();
         if (list.Count == 0)