mod-notify is not passing the "X-Okapi-Request-Id" header to its API calls

In order for Okapi to track API calls properly, the "X-Okapi-Request-Id" header should be passed along when the module makes its own API calls. Since this module is not using the RMB HTTP client, it needs to ensure that the header is passed to the vertx WebClient in "OkapiModulesClientImpl".

Without this header, the calls are disassociated with the initial call, like "check-out-by-barcode", making overall API performance analysis challenging.