1. Should there still be a --path-format flag?

If you specify "absolute" and "relative" in the keys, it won't
make sense to use it.

2. Should we consider a default option?

Some pros and cons:

- Pro: some values make more sense to be in absolute or relative
  format
- Pro: it's boring to always add `.(relative|absolute)` to the
  paths
- Con: it will be perpetuating what git-rev-parse does, and we
  don't git-repo-info to be git-rev-parse with a different
  interface. It's our chance to learn with [1] for example.
- Con: the user will need if the value is relative or absolute

3. Is printing both absolute and relative in a single call
  using --all acceptable?

If you're providing both keys, I think it's not only acceptable
but mandatory. `--all` should mean "all", not "all, but ...".

I have discussed these changes with both Justin and Lucas
internally. This series is presented to gather opinions from the
wider community before moving forward.

I probably sent the same comments internally, but I'm sending
here to share my opinions with the rest of the community ;-)

[1] fac60b8925 (rev-parse: add option for absolute or relative path formatting, 2020-12-13)