cli: add -o as shorthand for --name-only

[avamsi]

Would be easier to type when using with other commands -- of course, one
could always use an alias too, especially if -o is too confusing.

Checklist

If applicable:

• I have updated CHANGELOG.md
• I have updated the documentation (README.md, docs/, demos/)
• I have updated the config schema (cli/src/config-schema.json)
• I have added/updated tests to cover my changes

[yuja]

Do you want both jj log -o and jj diff -o? If the latter is what you use often, I think user alias is better. (FWIW, I tend to use --stat or --summary with jj log.)

[avamsi]

Yeah, I've never used jj log --name-only (didn't even realize it existed 😅) and I don't think I will (definitely not often enough to merit a shorthand). I could make the change just to be consistent, or just continue using an alias for jj diff --name-only (I'm leaving the PR open in case anyone's interested, but @yuja / other maintainers, please feel free to close).

---

jj log -s is definitely interesting, I use this script to do something similar:

print '@ Working copy changes:'
# We intentionally don't use bg(c) here to let jj automatically commit
# changes to the working copy (so it's not stale on output).
jj --color=always diff --summary --revision=@ | indent
conflicts=$(jj bgc resolve --list 2>/dev/null) && {
	print '\n\e[31mx Conflicts:\e[0m'
	print "$conflicts" | indent
}
print '\n| Parent commit changes:'
jj bgc diff --summary --revision='parents(@)' | indent
print
jj bgc log --revisions=interesting

[aliases]
        bg = [
                '--config=ui.log-word-wrap=false',
                '--ignore-working-copy',
                '--no-pager']
        bgc = ['bg', '--color=always']

Perhaps it's possible to simplify it now, I'll look at the changelog, thank you!