Stub value substitution using a template

[joelrosario]

What:

Introduce two templating features "{{REQUEST.QUERY-PARAMS.enabled}}" and "{{@DaTa}}", in order to coordinate values in example.

Why:

"{{REQUEST.QUERY-PARAMS.enabled}}" <- this allows a value from the request to be expected in the response. This way you won't have to provide multiple examples when the only difference is one value in the request and response, and they are coordinated.

"{{@DaTa}}" <- sometimes value A in the request should go with value B in the response. For example, let's say that when in the request JSON payload the value of department is engineering, the value of the location in the response JSON payload should be Bangalore, and the currency should be Rupees. This feature enables this coordination to be done in a single example file.

Checklist:

• Documentation added to the README.md OR link to PR on https://github.com/specmatic/specmatic-documentation
• Tests
• Sonar Quality Gate