Add a mu-plugin to enable permalinks without index.php in the URL

[sejas]

• Closes Support pretty permalinks #142

Proposed Changes

• Add a mu-plugin that enables having permalinks without the index.php in the URL.

Testing Instructions

• Apply this PR in your local machine
• Run nvm use && npm install && npm start
• In an existing or new site access Settings > Permalinks: /wp-admin/options-permalink.php
• Observe the given options does not have index.php
• Select any permalink
• Access the forntend page, click on the menu item Sample in the frontend.

Before	After

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[derekblank]

LGTM. With the changes applied using got_url_rewrite, I observed that permalinks without index.php were enabled. 🚀

trunk	add/permalinks

[wojtekn]

The code change looks clear, works as expected.