Accessibility: add a lang attribute to html #2348
Description
When analyzing datasette accessibility, one of the main (and easy to fix?) issue is the lack of lang attribute into thehtml tag: see https://qualweb.di.fc.ul.pt/evaluator/https%253A%252F%252Fglobal-power-plants.datasettes.com%252Fglobal-power-plants%252Fglobal-power-plants
The norm: https://www.w3.org/WAI/standards-guidelines/act/rules/b5c3f8/
Do we only have to fix: https://github.com/simonw/datasette/blob/main/datasette/templates/base.html ?
Is it ok to hard code this since datasette is only in English for the moment: <html lang="en">?