Moving a running xp from one grid to another (e.g. when refactoring) cancels the XP

I had a grid `grid_a` with too many experiments running so I refactored some of its experiments in a new grid file `grid_b`.
While running the new grid `dora grid grid_b` worked as expected and found the already running experiment, when I ran `dora grid grid_a` again it cancelled all the experiments that were now in `grid_b`.

It would be nice to have a way to track this scenario and only garbage collect experiments that are not linked to a grid.
And also it would be nice to ask the user for confirmation when cancelling experiments.

Start by tracing the `dora grid` command and its handling of running experiments and garbage collection. Reproduce moving a running experiment from `grid_a` to `grid_b`, then define how linked grids should prevent cancellation and when confirmation is required. Done means the moved experiments remain active and cancellation prompts the user.

Written by the indexing model from the issue text.