Bulk import customers from an CSV file.

The file must meet the following characteristics:

• CSV separated by commas
• Maximum 10,000 clients per import
• Maximum file size is 2MB
• Column names must be: Nombre, Apellidos, DNI, Email, Telefono, Nacimiento, Sexo, Grupo
• The Email is required
• The Nacimiento column is a date in DD/MM/YYYY format
• The Sexo column admits male or female
• In the Grupo column, if there are several, they must be separated with a semicolon (;)
• If the email already exists, the client is not imported