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

diff --cc Makefile
Simple merge

diff --cc object-file.c
Simple merge

diff --cc promisor-remote.c
Simple merge

diff --cc run-command.c
Simple merge

diff --cc run-command.h
Simple merge

diff --cc setup.c
Simple merge