Duplicate tab should create a new tab next to the original

Nobody has claimed this yet.

### Description of the new feature

At the moment, "Position of newly created tabs" allows "After the last tab" and "After the current tab". I prefer "After the last tab". However, when duplicating the current tab (expressly with "Duplicate tab", `Ctrl`+`Shift`+`d`), I find myself almost always dragging the new tab next to its original. It would be nice to have an intermediate setting (e.g. "After last except duplicates") that would behave like "After last", except it would behave like "After current" for tabs created with "Duplicate tab".

### Proposed technical implementation details

Implementing this would likely require that the information of whether the new tab creation was requested with the "Duplicate tab" command (and not e.g. by selecting the same profile again) survives to the point when the tab's location is decided.

Start by tracing the existing "Position of newly created tabs" setting and the "Duplicate tab" command through tab creation to where the new tab's location is decided. Confirm how duplicate requests can be distinguished from other tab creations, then update the setting behavior so duplicates appear next to the original while other new tabs retain the selected placement.

Written by the indexing model from the issue text.