RFC 619: (M1) Generate dependencies service skeleton (worker)
Created by: efritz
Modify the existing dependencies service to include (initially empty) missing components defined in RFC 619: Code Intelligence Data Platform.
Partially covers https://github.com/sourcegraph/sourcegraph/issues/33372. Originally drafted in https://github.com/sourcegraph/sourcegraph/pull/32473.
Test plan
N/A - all code is new and no-op'd.