chore(logs): Prefer Display over Debug for errors (#4790)

* chore(logs): Prefer Display over Debug for errors

The update to CONTRIBUTING.md said to prefer `Display` (%) for
formatting errors, but showed an example using `Debug` (?). I updated
the example to use % and switched all existing ? usage for errors to %.

Also switched from `error = %error` to the shorthand `%error`.

Follow up to https://github.com/timberio/vector/pull/4737

Signed-off-by: Jesse Szwedko <jesse@szwedko.me>

* cargo fmt

Signed-off-by: Jesse Szwedko <jesse@szwedko.me>