fix(docs): Document cargofmt

[marc2332]

Fixes #7317

cdd6ea5 added support for cargo fmt as formatter, but the docs were not updated, hence this PR.

I also renamed its name to be cargofmt.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

No duplicate PRs found

[rekram1-node]

@marc2332 can we update the docs and the code to both use "cargofmt" as the key? Ik that "breaks" the config but given how this wasnt even documented I think it's ok

[marc2332]

@marc2332 can we update the docs and the code to both use "cargofmt" as the key? Ik that "breaks" the config but given how this wasnt even documented I think it's ok

Sure! sec

[marc2332]

@marc2332 can we update the docs and the code to both use "cargofmt" as the key? Ik that "breaks" the config but given how this wasnt even documented I think it's ok

Done!