Reintroduce batch Collections operation via metadata panel

## Short description
Since https://github.com/guardian/grid/pull/3465, we may have lost the ability to edit Collections via metadata panel for when more than one image is selected. The only way to do that is by dragging. We should introduce this device available for one image to operate on selections of multiple too:

[This](https://github.com/guardian/grid/pull/3531) may be of help, but it would be great if the design of it would follow the current control and not look like editing Persons, Labels etc.

Start by examining the current single-image Collections control in the metadata panel and the changes from PR 3465. Review PR 3531 for a possible approach, then verify that the existing control supports selections of multiple images while retaining its current design and behavior.

Written by the indexing model from the issue text.