code: public PactDslRequestWithPath matchHeader(String header, String regex, String headerExample) {
          requestMatchers.addCategory("header").setRule(header, new RegexMatcher(regex));
          requestHeaders.put(header, Collections.singletonList(headerExample));
          return this;
      }
docs: Match a request header.
  
  @param header        Header to match
  @param regex         Regular expression to match
  @param headerExample Example value to use