Ability to edit/update slug

Currently, there is no way to edit or update a slug for a guest author, like you can for a regular post.

Start by locating the guest author editing flow and compare it with the existing regular post slug editing behavior. Trace where guest author slugs are stored and updated. Done means a guest author’s slug can be edited and saved reliably, matching the capability available for regular posts.

Written by the indexing model from the issue text.