[Discover][EuiDataGrid] Restore ability to compare documents

[kertal]

In legacy grid you could open/expand multiple documents, and had therefore a way to compare multiple documents (sort of). In the new data grid implementation this is no longer possible. During development of the new grid we implemented a way to select documents by checkbox in a PoC style, and removed later to focus on the stable parts.

So to allow users to select and compare documents in Discover the following should be implemented:

[ ] Add a checkbox to each document, allowing users to select/deselect document (We would store selected document ids in the Browsers sessionStorage, for a first version this would work like an additional filter based on the 500 doc sample. In later interactions this could work like a document collector, so you could collect document using differers filters and queries )
[ ] Provide a button/switch to the data grids toolbar to just view this selected documents
[ ] Provide a navigation for users to navigate between open documents (PR #94439)

It could look like this:

This would allow users to compare documents and fields in a already better way than in legacy word

• Would solve: Picking some documents to compare of a large set
• Wouldn't solve: Expanding all documents of a small set, to get an overview

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[kertal]

PR #94439 adds document navigation in the flyout, so users don't need to expand multiple documents like in the legacy world

[kertal]

This was already implemented, closing this