[keyserver] Revise dc.sh passed parameters

Summary:
Relevant Linear issue with full context here.

This diff cleans up dc.sh by revising the passed parameters to docker compose. They should be double quoted to properly expand the argument list. Additionally, the @ parameter can be used singularly without curly braces (see inline comment).

This script was initially introduced a few weeks ago in D4213, adding those reviewers here.

Test Plan: ShellCheck, close reading.

Reviewers: atul, ashoat, palys-swm

Reviewed By: ashoat

Subscribers: palys-swm, Adrian

Differential Revision: https://phab.comm.dev/D4367