consider a somewhat more permanent storage of the output/error notes from installation

[njtierney]

It's good we've got

greta_notes_conda_create_error()
greta_notes_conda_create_output()
greta_notes_conda_install_error()
greta_notes_conda_install_output()
greta_notes_install_miniconda_error()
greta_notes_install_miniconda_output()

However these are wiped after an R restart - it would be neat if there was a better default place to store them so they can be inspected later, however, that might also be a bit rude to save files on someone's computer without them giving proper permission.

[njtierney]

Instead of having 6 functions to inspect the installation process, we should have a single log file that gets written to. This can be specified with a special ENVVAR, and then a function to set that envar to make it easier for users.

This means we can instead have a function that specifies how to set this if you want to, which you will only generally do once you have a failed install. It should also reduce complexity by only having one thing to maintain/touch.

The file that gets written to will have the text appended to the same file each time.

In the interim there could be an internal greta object that logs all the errors, potentially saving it to a temporary file, so we can identifying potential errors in installation log files.

[njtierney]

Related to #493