Script Generator: Combine "Generate" and "Generate As" buttons into one "Save As"

As a Muon scientist/user, I would like the "Generate Script" and "Generate Script As" buttons to be combined into one "Save As" to save space and simplify the UI.

# Acceptance Criteria

- [ ] "Save As" button defaults to the current script location, enabling the user to overwrite it.

Might need to check with other scientists if this will have undesired sideffects or not.

# How to Test
verbose instructions for reviewer to test changes
(Add before making a PR)