docs: updated script urls to point to v0-3-branch subdomain of website

[louis-bourgault]

PR check-list

• [X ] Branch has a clean commit history
• [ X] Additional tests are included, if changing behaviors/core code that is testable.
• [ X] Proper Copyright + License headers added to applicable files (Generally, we stick to "The ZMK Contributors" for copyrights to help avoid churn when files get edited)
• [ X] Pre-commit used to check formatting of files, commit messages, etc.
• [X ] Includes any necessary documentation changes.

[caksoylar]

I don't think we want to do this, we intentionally removed the setup scripts and replaced them with a pointer to ZMK CLI. (The CLI initializes repo with latest release by default.)

That being said, the v0.3 docs pointing to non-existent scripts isn't great, for sure. It'd be a better solution if someone could cherry-pick all docs commits related to ZMK CLI transition into the v0.3-branch.

[joelspadin]

I was working on suggesting the same thing, but you beat me to it. See #3137 and #3209 for the main changes to the documentation that switched from these scripts to ZMK CLI.