Suppress MAR fallback noise in Save/Install and remove test-oriented information output

[Copilot]

When MAR is searched before other repositories, normal 404 Not Found responses for packages not present in MAR were being emitted as user-visible errors, even when a later repository could satisfy the request. In addition, container registry auth-path internals were emitting Information-stream messages used only by tests.

• Container registry fallback error classification

  • Updated ContainerRegistryServerAPICalls.GetHttpResponseJObjectUsingDefaultHeaders(...) to classify ResourceNotFoundException as:
    • FullyQualifiedErrorId = "PackageNotFound"
    • ErrorCategory = ObjectNotFound
  • This aligns MAR 404 behavior with existing fallback logic so per-repository misses do not surface as misleading user errors during multi-repo search.

• Removed test-only Information stream output

  • Replaced WriteInformation("Value of isRepositoryUnauthenticated: ...") with WriteDebug(...) in container registry auth flow.
  • Eliminates noisy Information output from normal cmdlet usage while preserving diagnosability via Debug stream.

• Adjusted affected tests to match intended behavior

  • Updated publish/save/install tests that previously asserted MAR fallback noise or relied on Information-stream internals.
  • New expectations validate no extra error/info output for successful fallback scenarios.

catch (ResourceNotFoundException e)
{
    errRecord = new ErrorRecord(
        exception: e,
        "PackageNotFound",
        ErrorCategory.ObjectNotFound,
        _cmdletPassedIn);
}

• Fixes Multiple Cmdlets emits unneeded log/errors #1993

[azure-pipelines]

Azure Pipelines:
There may be pipelines that require an authorized user to comment /azp run to run.