Migrate functionality using pak instead of remotes

[psolymos]

Use pak, see: https://pak.r-lib.org/reference/pak_package_sources.html

Reason: this usethis post says https://usethis.r-lib.org/articles/git-credentials.html#what-about-the-remotes-and-pak-packages

Lifecycle-wise, remotes is being replaced by pak, but we are still in the transition period, where both are maintained.

Urgency: not too urgent but need to start thinking.