Consider a which program before downloading #68
Description
Problem to be solved
The obolup.sh script doesn't check if a program exists in the path, and just begins downloading and installing once there aren't binaries in OBOL_BIN_DIR. this puts multiple programs into the path and a user might end up using the binary they didn't expect.
https://github.com/ObolNetwork/obol-stack/blob/main/obolup.sh#L347
[Optional] Proposed solution
Check if the installed version has the OBOL_BIN_DIR in its path before moving to installing newer vesions. If the program exists and the which is elsewhere. Log that an alternative installation for X is already installed, and should be managed using the existing method.
Stretch goal but decent UX improvement would be still telling the user that their externally managed version of X is out of date or not even if we don't touch it.