Make overwriting script keys optional

[kordwarshuis]

• What: Spec-Up-T update procedure writes keys / value pairs to the script section in package.json. However it does not overwrite keys.
• Why: This is a good approach but sometimes we do want to overwrite keys, for example when a path has changed.
• What way: modify script so we can pass argument that instructs per key to overwrite or not, default: not
• Where: https://github.com/trustoverip/spec-up-t/blob/master/src/install-from-boilerplate/add-scripts-keys.js