List of nodes created from the template

I have removed all link templates for content_template entity type, so that it is not possible to view, edit, delete it directly. Everything is done only through node/<nid>/template and node/templates pages.

I have added new route node/<nid>/overview (and tab "Created from this template") that has the list of content that was created from this template:

Also now the template node from which content was created is stored in the field 'template' that is part of node entity storage now, no key_value storage is used anymore, as it is not possible to create overview page from it. The update is provided to copy the data from key_value collection content_templates to newly created field template

The functionality works, but I think there could be some improvements:

On the path /admin/content/template there should be a column, indicating if a template is active or not. I only have one template in my local installation, but I see two. The latter was used in the past, but was deactivated.

On the path /node/766/overview the title should be linked, so it is consistent

I would also change the text in the tab and the actions to "Descendants". If possible this tab should come aver "Templates". They could be positioned in the back.

I have added new column to templates list and adjusted display of existing columns, please check again.