[services] Tunnelbroker - Change AmqpManager.send() method arguments to use MessageItem in tests

Summary:
This diff introducing changes in tests for AmqpManager.send() method to use MessageItem instead of arguments list.
The function changes was introduced in D4511.

Linear task: ENG-1214

Test Plan: Run tests using yarn run-unit-tests.

Reviewers: karol, tomek

Reviewed By: tomek

Subscribers: ashoat, tomek, adrian, atul, karol, abosh

Differential Revision: https://phab.comm.dev/D4512