When moving or rearranging dashboard cards, allow a card to be inserted in a place where there isn't currently space for it

[mazameli]

Right now it's really painful trying to rearrange questions on a very full dashboard, especially when trying to move a newly added question to the top — you have to create space manually by moving every single other card down, one by one, to make room for the new card.

A pretty straightforward solution would be to add an insertion line interaction that would insert rows on mouse-up to make room for the card being dragged, pushing the other cards down.

Here's a clickable prototype of the concept, and a screenshot that gives you the gist:

Possible alternatives

Versus the below, I think the above is better as it feels more direct and intuitive without being overly twitchy.

• Add a control to insert blank space/rows into a dashboard manually.
• Make it possible to select and move multiple cards at once via a click and drag or command/shift+click interaction.
• Bring back the old card reshuffling behavior that was in the early versions of Metabase (this was pretty annoying).

[flamber]

Related to #9895