NSIS: `/AddToPath` and `/RegisterPython` always available

[jaimergp]

Checklist

• I added a descriptive title
• I searched open reports and couldn't find a duplicate

What happened?

I noticed these CLI options are always available and parsed, regardless the value of initialize_conda and register_python. This means they show up in the help message and can induce parsing errors even when they should be totally ignored.

Additional Context

No response