[inference] parameter generation

[earldouglas]

For inferred tests, it would be handy to allow users to tell swagger-test how to generate values for path parameters.

e.g. get /foo/{bar}/baz needs a way for the user to provide sample values for {bar}

This pattern applies in lots of other places too, including query parameters, headers, form fields, body models, etc. Split these cases into separate issues as they materialize.

[earldouglas]

Possibly useful for this: jsverify