[comm-lib] Add missing feature dependency to Cargo.toml

Summary: Noticed that this was missing and compilation failed for services with enabled blob-client feature, but disabled http feature.

Test Plan: cargo build -p comm-lib --all-features

Reviewers: varun, will, kamil

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D13649