[services] Tunnelbroker - Add test for putMessageItemsByBatch function

Summary:
This is a test for putMessageItemsByBatch function introduced in D4378.
In this test, we are creating a messages batch of 29 items and putting them into the database by the putMessageItemsByBatch function. We are expecting the
size of the found items would be the same as an item's batch size.

Linear task: ENG-1301

Test Plan: Run yarn test-tunnelbroker-service-dev-mode

Reviewers: karol, tomek

Reviewed By: tomek

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

Differential Revision: https://phab.comm.dev/D4377