Split collections geometry

Like it's done in the metacatalog, split collections geometry if pictures are too far apart.

The limit used is ~50m.

The huge problem is that thus a collection might have a null geometry if all points are far from each others (and thus the collection will not have a bbox).

I'd be in favor of using a geometry instead of a multilinestring, tp be able to also have separate points, but we already had this conversation, so I guess it's not that big of a deal (and a collection with only 1 picture already doesn't have neither a geometry nor a bbox).

Note: there is not yet the SQL migration splitting all existing geometry, it will be in a separate MR to apply it in a future version.