[Feature]: option to install pkg dependencies in r cmd check workflow

[k-doering-NOAA]

Is your feature request related to a problem? Please describe.

Some R packages have dependencies on other software that is not an R package or not hosted on Cran or Github (e.g., INLA, various linux utilities). These dependencies usually aren't obvious until trying to run r cmd check on a github action runner.

It would be useful for users to be able to input dependencies into the ghactions4r r cmd check workflow, as currently this cannot be done and users have to instead maintain their own r cmd check workflows.

Describe the solution you would like.

allow users to optionally input dependencies to the r cmd check workflow. This needs to be thought out given that r cmd check runs 3 different OSes, and dependencies could vary between mac, linux, and windows.

Describe alternatives you have considered

provide documentation for users to set up their own workflow and not use ghactions4r (or just clearly state that it is out of scope for the pkg).

Since this is a common use case, this doesn't feel out of scope.

Additional context

No response