Add lastModifiedDate to document tree

[fynnfluegge]

Currently the lastModifiedDate is only available in each document from the api as:

{
  "id":"someId",
  "parentId":"someParent",
  "userId":"userId",
  "title":"some title",
  "content":"some content",
  "lastModifiedDate":"2024-11-13T22:05:58.6491204Z",
  "deleted":false,
  "isPublic":true
}

The lastModifiedDate should be also added in the document tree as:

{
  "id":"someId",
  "documents": [
   {
      "id":"someId",
      "name":"title",
      "parent":"root",
      "pinned":true,
      "lastModifiedDate":"2024-11-13T22:05:58.6491204Z",   // <---- here
      "children":null
    },
    ...
  ]
}

For this save also the document tree in save-document-handler with the lastModifiedDate