[services] Get rid of return std::move(...) in services codebase
Summary:
Context: https://linear.app/comm/issue/ENG-619/get-rid-of-stdmove-in-the-services-codebase
https://developers.redhat.com/blog/2019/04/12/understanding-when-not-to-stdmove-in-c
https://phabricator.ashoat.com/D2912?id=8614#inline-15820
https://phabricator.ashoat.com/D2876?id=8631#inline-15961
NOTE: We don't want to remove std::move altogether, just when we're returning so we don't interfere with return value optimization. We're still going to need to std::move unique_ptrs into lambdas and whatnot.
Test Plan: CI and close reading and previous discussion
Reviewers: tomek, marcin, kamil, inka, varun, max, jon, O2 Blocking Reviewers, ashoat
Reviewed By: max, O2 Blocking Reviewers, ashoat
Subscribers: ashoat, abosh
Differential Revision: https://phab.comm.dev/D5608