Restore missing table footers

What does this MR do and why?

Fixes Table caption and footer are gone (#632638 - closed), scoped to footer. Regression introduced in Render plain HTML table (no GlTable) Vue compon... (!239559 - merged).

Restores <tfoot>, which was dropped because only <thead> / <tbody> were carried over when tables were replaced with sortable tables.

Screen recordings

Footer stays put when sorting:

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