Add option "Display within Directus" in the custom links of the module bar

Summary External links are always open in a new browser window. To add custom dashboards (eg Grafana etc) or additional admin sites related to the project, it would be nice to handle that without "leaving" the Directus UI frame. So adding the Option "Display within Directus" in the custom links of the module bar would make it possible to implement an easy way to add other admin pages under the directus hood. Basic Example _No response_ Motivation Just add a easy to implement feature to make Directus the main admin page for a project. Detailed Design Adding the Option "Display within Directus" checkbox in the custom links of the module bar. Requirements List Must Have: • Adding the Option "Display within Directus" checkbox in the custom links of the module bar. Drawbacks • It's an easy one without big effort Alternatives • Less comfort when users have to combine different admin pages. Not everything is possi…