Feature: #93423 - Show warning about duplicated root pages in sites module

See forge#93423


It might happen that the same root page ID is configured for multiple site configurations, e.g. in case corresponding files were copied manually. This might lead to misbehavior, since always the last site with this root page ID defined is used by TYPO3. As such configuration errors might be hard to spot, the Sites module now informs about such duplications in the site configuration overview view.


The site module now warns administrators in case the same root page ID is used in multiple site configurations.