Allows passing of regex type (#832)

without this change if one does $(regex("[0-9]")) we have no knowledge of whether the result should be text or a number. What we do ATM is we always generate a String
with this change once can pass the type of regular expression and we will generate the concrete value of that given type

fixes gh-768

samples/standalone/dsl/http-server/src/test/resources/contracts/fraud/shouldReturnFraudStats.groovy

@@ -12,7 +12,7 @@ import org.springframework.cloud.contract.spec.Contract
 			response {
 				status OK()
 				body([
-						count: 200
+						count: $(regex("[2-9][0-9][0-9]").asInteger())
 				])
 				headers {
 					contentType("application/json")