New Group Layout Option: Container

<!-- Please only use this template for submitting feature requests --> **Why is this needed**: I frequently find myself designing dashboards that repeat panels based on a variable. More and more, there is a request from dashboard users to have dashboards that repeat pairs of panels. The important issue here is that the two panels (e.g., one table and one time series view) should be shown next to each other in order to provide context. Currently I have two options: - Repeat all tables and all time series individually (based on the same dashboard variable). This shows all panels, but loses the pairwise context between them. <img width="968" height="762" alt="Image" src="https://github.com/user-attachments/assets/d1960753-8614-48a5-b6fa-250f0268eb92" /> - Place a table and a timeseries into a row (or now a tab) and repeat the group. This produces large amounts of white space on screen if the two panels do not fill the whole width. <img width="824" height="739" alt="Image" src="https://github.com/user-attachments/assets/1b2e8add-befe-4389-845d-f7bd330ec5fe" /> **What would you like to be added**: I envision a new group layout that I'll "container" here. A container should function almost like a row -- with the only exception that containers are not full-width, but only as wide as the contained panels. This allows containers to repeat like individual panels (horizontal first, with automatic breaks to new lines). <img width="1133" height="450" alt="Image" src="https://github.com/user-attachments/assets/1f32fb89-d254-4375-b573-aba273c5d819" /> **Who is this feature for?** Anybody who needs to present different views on the same/related data and wants to achieve a dashboard layout that keeps related information close while avoiding large amounts of whitespace (and hence scrolling).