Unify add to agenda option for motion, assignment and motion block

[Elblinator]

Current behavior
If you add a motion/assignement or motion block to the agenda (via the detail view and the three dot menu) the object is added at the end of an agenda

And assignments cannot be added via multi-select

And a motion via the multi-select the visiblity cannot be decided what the visibility is

Wanted behavior

• The following objects should hav a "add to Agenda" option in the the three dot menu
  • motion-detail
  • motion-list multi-select
  • assignment detail
  • assignment-list mullltiselect
  • motion blcok detail
• This option should open a dialog
• The dialog should have the following things inside of itself:
  • Title:
    • In detail view: "[title in detail view]: move to agenda"
    • in Multi: "Move all selected items to agenda"
  • The agenda visibility combox box
  • A "Parent agenda item" Combobox where you can select every item in the agenda

Additional context
inspired by #2147

[Elblinator]

I will remove the following part from this Issue

Dialog:
   - [ ] A checkbox with the description "Set topic as parent"
      - If this checkbox is ticked the "topic above" selected item should be set as parent
      - If the ckeckbox is not ticked then the item should be sorted into the topic at the same level but below the "topic above"

I assume that the backend needs to add this field, whoever will implement this can try to make it work, but as I asid I assume that sth is still missing for that part of the backend

Everything else can already be worked on