From: ZheNing Hu <adlternative@gmail.com>

Add a new option --format that output index enties
informations with custom format, taking inspiration
from the option with the same name in the `git ls-tree`
command.

--format cannot used with -s, -o, -k, -t, --resolve-undo,
--deduplicate and --eol.

Signed-off-by: ZheNing Hu <adlternative@gmail.com>

Submitted-As: https://lore.kernel.org/git/pull.1262.v5.git.1657002760815.gitgitgadget@gmail.com
In-Reply-To: https://lore.kernel.org/git/pull.1262.git.1655300752.gitgitgadget@gmail.com
In-Reply-To: https://lore.kernel.org/git/pull.1262.v2.git.1655629990185.gitgitgadget@gmail.com
In-Reply-To: https://lore.kernel.org/git/pull.1262.v3.git.1655777140231.gitgitgadget@gmail.com
In-Reply-To: https://lore.kernel.org/git/pull.1262.v4.git.1656257376109.gitgitgadget@gmail.com