Merge branch 'jt/partial-clone-submodule-1'

Prepare the internals for lazily fetching objects in submodules from their promisor remotes. * jt/partial-clone-submodule-1: promisor-remote: teach lazy-fetch in any repo run-command: refactor subprocess env preparation submodule: refrain from filtering GIT_CONFIG_COUNT promisor-remote: support per-repository config repository: move global r_f_p_c to repo struct