Custom Dashboards: introduce pagination for List widget

[antoinemzs]

Breakout of #2885

Context

Some queries projected onto the List widget may return a large number of options, leading to long scrolls.

Use case

Peruse a large dataset in the list widget, in keeping with good performance.

Current Workaround

All items are dumped into the list, capped to 100.

Proposed Solution

Pagination controls on the List widget and syntax for passing pagination parameters to the backend. Each page is a capped set of e.g. 20, 50, 100.