Rename format option to output-format

[zanieb]

The format option could be confused with our formatter. It should be renamed to output-format in both the configuration file and CLI e.g.

--format <kind> -> --output-format <kind>
format = <kind> -> output-format = <kind>

The previous name should undergo a deprecation period during which we display a warning on use.

[zanieb]

I think we'll want to look into building tooling for rename deprecations in our configuration macro.