From: =?UTF-8?q?Max=20=F0=9F=91=A8=F0=9F=8F=BD=E2=80=8D=F0=9F=92=BB=20Copl?=
 =?UTF-8?q?an?= <mchcopl@gmail.com>

Note to reviewer: I hate the name `--header-or`!  Please help me come up
with a better name.

Summary:
This change adds a new option to `git log` that allows users to search
for commits that match either the author or the commit message. This is
useful for finding commits that were either authored or co-authored by a
specific person.

Currently, the best way to find a commit either authored or co-authored
by a specific person is to use

```sh
echo \
    $(git log --author=Torvalds --pretty="%cd,%H\n" --date=iso-strict) \
    $(git log --grep="Co-authored-by: .*Torvalds" --pretty="%cd,%H\n" --date=iso-strict) \
| sort -n --reverse \
| awk -F, '{print $2}' \
| tr '\n' '\t' \
| xargs git show --stat --stdin
```

This is a bit of a pain, so this change adds a new option to `git log`.
Now finding either authors or co-authors is as simple as

```sh
git log --author=Torvalds --grep=Torvalds --header-or
```

Test plan:
1. create commit authored by A and co-authored-by B
2. create commit authored by B
3. run `git log --author=B --grep="Co-authored-by: B" --header-or`
4. expect to see both commits

Signed-off-by: Max 👨🏽‍💻 Coplan <mchcopl@gmail.com>

Submitted-As: https://lore.kernel.org/git/pull.1710.git.1712353687464.gitgitgadget@gmail.com