Add usage of negation in the phone_calls example

[sorsaffari]

Problem to Solve & Current Workaround

Prior to introducing negation in Graql, we had an attribute called is_customer assigned to a person in the phone_calls schema. This was done as a workaround in the absence of negation.

Proposed Solution

Use the newly introduced negation pattern in the query that relies on the is_customer attribute of person.

Additional Information

N/A