Refactor DataTable to handle internal scrolling and fix overflow on narrow viewports

[choo121600]

The DataTable component previously rendered a Fragment (<>), delegating scroll behavior to individual consuming pages.
Pages like Connections, Variables, AssetsList, and DagsList wrapped DataTable in <Box overflow="auto">, which caused two issues.

1. On narrow viewports, horizontal scroll was limited to the table area and content could be clipped.
2. Vertical scroll moved the entire DataTable (including heading and pagination) instead of just the table body.

This PR moves scroll handling into DataTable itself

Before

Screen.Recording.2026-02-28.at.2.03.12.PM.mov

After

Screen.Recording.2026-02-28.at.2.02.33.PM.mov

Screen.Recording.2026-02-28.at.2.09.51.PM.mov

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