[Discover] Add "Chart options" menu

[andreadelrio]

To support the integration with ML's Data Visualizer, we've added a new toggle (button group) to the top section of the main area of Discover. This has caused that top area to start getting quite crowded. The proposed solution for this is:

1. Add a new menu labeled "Chart options" which has the items a) toggle chart visibility and b) set time interval for chart. Align this menu to the right.
2. Center the toggle to switch between views (i.e. Documents view / Aggregated view)
3. (not in screenshot) Consider replacing the x-axis label with the time range OR adding the time range next to the x-axis label
4. (not in screenshot) Remove the "Count" label of the y-axis of the chart

Here's a prototype to better show the proposed changes

Blocks #107184

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)