[services] Tunnelbroker - Empty field checks in database items

Summary:
Check multiple fields to not be empty in the database item entity.

Implemented a small checkEmptyField function in Tools which checks for an empty string and zero numbers.
Usage implementation in database items also was added.

Linear task: ENG-618

Test Plan: Successfully built and run service using yarn run-tunnelbroker-service.

Reviewers: palys-swm, karol-bisztyga, varun

Reviewed By: palys-swm

Subscribers: ashoat, palys-swm, Adrian, atul, karol-bisztyga, benschac

Differential Revision: https://phabricator.ashoat.com/D3525