ds/sparse-checkout-requires-per-worktree-config (was Re: What's cooking in git.git (Jan 2022, #04; Fri, 14))

> * ds/sparse-checkout-requires-per-worktree-config (2022-01-14) 6 commits
>  - worktree: copy sparse-checkout patterns and config on add
>  - sparse-checkout: use repo_config_set_worktree_gently()
>  - config: add repo_config_set_worktree_gently()
>  - worktree: add 'init-worktree-config' subcommand
>  - config: make some helpers repo-aware
>  - setup: use a repository when upgrading format
> 
>  "git sparse-checkout" wants to work with per-worktree configration,
>  but did not work well in a worktree attached to a bare repository.
> 
>  Expecting an update.
>  cf. <1db0f601-4769-15c0-cd58-ecddfa1fc9d5@gmail.com>
>  source: <pull.1101.v3.git.1640727143.gitgitgadget@gmail.com>