input: Write a python function to add a new customer to the MongoDB collection ensuring unique values for 'Name', 'Phone Number', 'Email', and 'Address'.
  assert add_customer('John Doe', '123-456-7890', 'john.doe@example.com', '123 Elm Street') == "Customer added successfully"
  assert add_customer('Jane Doe', '987-654-3210', 'jane.doe@example.com', '456 Oak Avenue') == "Customer added successfully"
  assert add_customer('John Doe', '123-456-7890', 'john.doe@example.com', '123 Elm Street') == "Customer already exists"
output: def add_customer(name, phone, email, address):
      from pymongo import MongoClient, errors
      
      client = MongoClient('mongodb://localhost:27017/')
      db = client['mydatabase']
      customers = db['customers']
      
      existing_customer = customers.find_one({
          "$or": [
              {"Name": name},
              {"Phone Number": phone},
              {"Email": email},
              {"Address": address}
          ]
      })
      
      if existing_customer:
          return "Customer already exists"
      
      new_customer = {
          "Name": name,
          "Phone Number": phone,
          "Email": email,
          "Address": address
      }
      
      try:
          customers.insert_one(new_customer)
      except errors.DuplicateKeyError:
          return "Customer already exists"
      
      return "Customer added successfully"