* Extract OrganizationService.SignupClientAsync into new ResellerClientOrganizationSignUpCommand
* Refactor ResellerClientOrganizationSignUpCommand to remove unused dependencies and simplify SignupClientAsync method signature
* Add unit tests for ResellerClientOrganizationSignUpCommand
* Rename SignUpProviderClientOrganizationCommand
* Rename ProviderClientOrganizationSignUpCommand
* Register ProviderClientOrganizationSignUpCommand for dependency injection
* Refactor ProviderService to use IProviderClientOrganizationSignUpCommand for organization signup process
* Refactor error handling in ProviderClientOrganizationSignUpCommand to use constants for error messages
* Remove SignupClientAsync method from IOrganizationService and OrganizationService, along with associated unit tests
