Protected packages: Fix documentation for protection rules

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What does this MR do and why?

This MR fixes a few small issues in the protected packages documentation:

• It correctly sets the heading to ## for the PATCH endpoint. Previously it was ###, which meant it was grouped under POST
• It fixes the path for protected package rules on the index site api_resources.md
• It adds the PATCH request type to the list of REST API status codes, since we are using it for protected packages.

Issue: #457512 (closed)

🛠 with ❤ at Siemens

MR acceptance checklist

MR Checklist ( @nwittstruck)

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the javascript style guides
• Conforms to the database guides

Screenshots

Related to #457512 (closed)