* Implement ResellerClientOrganizationSignUpCommand for signing up reseller client organizations with email invitations and error handling
* Refactor ProvidersController to replace IOrganizationService with IResellerClientOrganizationSignUpCommand for organization sign-up process
* Remove CreatePendingOrganization method from IOrganizationService and its implementation in OrganizationService
* Add IResellerClientOrganizationSignUpCommand to service collection for organization sign-up
* Add comment to clarify organization deletion process in ResellerClientOrganizationSignUpCommand
