[services] Move gtest to base image

Summary: Moving gtest package to the base image as it is going to be used by all services anyway, the package's small and doing this we avoid repetition(we'd otherwise have to add this to every service's Dockerfile)

Test Plan: cd services && yarn build-all

Reviewers: palys-swm, geekbrother, ashoat

Reviewed By: palys-swm, ashoat

Subscribers: ashoat, palys-swm, Adrian, atul, boristopalov

Differential Revision: https://phabricator.ashoat.com/D2692