R: If R_HOME isn't set, try R RHOME command #2111
Description
I think it'd be very useful to retrieve R_HOME from the R found in PATH, if not already set. This will make the usage of Ark as a Jupyter kernel easy and frictionless.
From @lionel-
To be done as a follow up to posit-dev/ark#205
We already do this for the testing variant of start_r(), so we should be able to unify the approach with our "real" start_r()