Updated namespaces for `CreateEnvelopeReceiverCommand` and related classes to `EnvelopeGenerator.Application.EnvelopeReceivers.Commands.CreateEnvelopeReceiver` for better organization and clarity.
- Updated namespaces in `CreateEnvelopeReceiverCommand`, `CreateEnvelopeReceiverCommandHandler`, and `CreateEnvelopeReceiverResponse`.
- Adjusted imports in `MappingProfile.cs`, `EnvelopeReceiverService.cs`, and `Fake.cs` to reflect the new namespace.
- Modified `EnvelopeReceiverController.cs` to use the updated namespace and simplified type reference in a `foreach` loop.
