docs: Replace user setup script with ZMK CLI (#3137)

This deletes the Bash and PowerShell setup scripts in favor of using
ZMK CLI. The old setup scripts are broken, since the config repo
template uses ZMK version 0.3, while the setup scripts use hardware
metadata from the main branch. ZMK CLI doesn't have this issue, because
it clones the version of ZMK listed in the config repo to get hardware
metadata.

Much of the "Installing ZMK" page has been rewritten to give
instructions for installing ZMK CLI and using it to create and modify
a config repo. The previously-hidden page on ZMK CLI has been added to
the sidebar and repurposed into general documentation for the tool.

docs/docusaurus.config.js

@@ -49,7 +49,6 @@ module.exports = {
     path.resolve(__dirname, "src/hardware-metadata-collection-plugin"),
     path.resolve(__dirname, "src/hardware-metadata-static-plugin"),
     path.resolve(__dirname, "src/hardware-schema-typescript-plugin"),
-    path.resolve(__dirname, "src/setup-script-generation-plugin"),
   ],
   themeConfig: {
     colorMode: {