No way to change OPAMROOT during installation

[jonahbeckford]

Although it is safer to ignore prior variables during an install, OPAMROOT should be settable to another location to save space.

Perhaps make it a variable in a sexp file with a USERNAME wildcard so it can be set by administrators.

[jonahbeckford]

Also, even when OPAMROOT is a Machine environment variable, dkml init still uses the default opamroot:

# Run eval $(opam env '--root=C:\Users\beckf\AppData\Local\opam' '--switch=Y:\source\dkml-workflows') to update the current shell environment