[services] Clean up run_service.sh using ShellCheck

Summary: Related Linear issue here. This is part of a set of diffs that will allow ShellCheck to be added to the CI. See inline comments for specific details of the ShellCheck error/warning output.

Test Plan: ShellCheck

Reviewers: atul, jon, tomek

Reviewed By: atul, jon, tomek

Subscribers: max, ashoat, adrian, karol

Differential Revision: https://phab.comm.dev/D4723