Detect that people need customer support using Built-in NLP

#### Is your feature request related to a problem? Please describe.
Currently, If a person send a text message containing the keyword `help`, we will trigger the customer care flow, but this does not cover other type of support request. See https://github.com/fbsamples/original-coast-clothing/blob/master/services/receive.js#L92

#### Describe the solution you'd like
We should detect that a person needs help using a custom Built-in NLP model, and route them accordingly to the correct experience.

#### Documentation
- https://developers.facebook.com/docs/messenger-platform/built-in-nlp/#customizing_nlp