Merge branch 'cs/add-skip-submodule-ignore-all'

"git add <submodule>" has been taught to honor submodule.<name>.ignore that is set to "all" (and requires "git add -f" to override it). * cs/add-skip-submodule-ignore-all: Documentation: update add --force option + ignore=all config tests: fix existing tests when add an ignore=all submodule tests: t2206-add-submodule-ignored: ignore=all and add --force tests read-cache: submodule add need --force given ignore=all configuration read-cache: update add_files_to_cache take param ignored_too