Fix: Table question's columns panel forces the whole page to scroll w…

[UncleTomsCabi]

…ith many columns

Problem

When a Table question has enough columns to overflow the viewport (reproduced with 7 columns), reaching the last ones requires scrolling the whole page instead of just the columns panel. Because the panel is a Bootstrap dropdown menu, scrolling the page while it stays open can make it jump back to the top instead of staying anchored to its toggle button, making it effectively impossible to configure columns past a certain point.

Fix

Give the columns container its own scroll (max-height: 60vh; overflow-y: auto) instead of letting it grow past the viewport. The "Add column" button stays outside the scrollable area and is always visible.

Testing

Added a regression test (TableQuestionAdminConfigRenderingTest) asserting that the rendered admin template's columns container carries both overflow-y: auto and a max-height constraint — a bare overflow-y: auto with no height limit never actually scrolls, so both are checked together.

[Rom1-B]

@UncleTomsCabi Entry is too long for a changelog line; shorten to the gist of the fix.

Suggested change

	- Fixed the `Table` question's columns configuration panel: with enough columns to overflow the viewport, reaching the last ones required scrolling the whole page, which could make the still-open dropdown menu jump back to the top instead of staying anchored to its toggle button. The panel now scrolls on its own
	- Fixed the `Table` question's columns configuration panel forcing the whole page to scroll instead of scrolling on its own