[dockerignore] Add missing entries

Summary: Noticed that many things weren't dockerignored, especially the target directories in services (Rust build artifacts dir)

Test Plan: CI docker builds, also seen improvement in docker build context size.

Reviewers: jon, varun, michal

Reviewed By: michal

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D9036