Fix logic of marking task as failed (#3083)

* Fix logic of markaing task as failed
- Do not mark task as failed if it is already in the shutting down state
- accumulate errors when setting task error to understand the context
- refactor the Error record

* fix tests

* format

* Fix build

* Update src/ApiService/ApiService/onefuzzlib/ImageReference.cs

Co-authored-by: George Pollard <porges@porg.es>

* Update src/ApiService/ApiService/onefuzzlib/ProxyOperations.cs

Co-authored-by: Teo Voinea <58236992+tevoinea@users.noreply.github.com>

---------

Co-authored-by: George Pollard <porges@porg.es>
Co-authored-by: Teo Voinea <58236992+tevoinea@users.noreply.github.com>

src/ApiService/IntegrationTests/Fakes/TestEndpointAuthorization.cs

@@ -36,9 +36,9 @@ sealed class TestEndpointAuthorization : EndpointAuthorization {
 
         return _context.RequestHandling.NotOk(
             req,
-            new Error(
+            Error.Create(
                 ErrorCode.UNAUTHORIZED,
-                new string[] { "Unrecognized agent" }
+                "Unrecognized agent"
             ),
             "token verification",
             HttpStatusCode.Unauthorized