[services] Change sourcing bash in scripts

Summary: https://linear.app/comm/issue/ENG-1087/change-sourcing-bash-in-scripts-for-services

Test Plan:

cd services
yarn test-backup-service-dev-mode
yarn test-blob-service-dev-mode
cd ..
git grep "#\!/bin/bash" # should be empty

Reviewers: palys-swm, ashoat

Reviewed By: ashoat

Subscribers: jonringer-comm, ashoat, palys-swm, Adrian, atul, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3981