git_default_branch_rename() could attempt to set the codecov default too? (or give the user an AI to do so)

[MichaelChirico]

Just encountered this:

r-lib/bit64#104

I was able to update master->main as the default branch in git, but Codecov does not automatically pick up these changes (so that when you browse to the repo on Codecov, it looks like coverage has not changed since the last commit to the old master). It took several days to notice that this is wrong.

Therefore it would be nice if this function could also work to update codecov/inform codecov of the change.

It might be overkill to add codecov API support from scratch if there's nothing using that so far in {usethis}. In that case, just writing something in the console like "Don't forget to manually update the default branch in Codecov, follow these steps" would still be good, ideally after detecting that {covr} is used for this repo.