Complete accessibility improvements to allow us to integrate eslint-plugin-jsx-a11y

[umpox]

Feature request description

Plugin PR sourcegraph/eslint-config#170
Current errors: https://buildkite.com/sourcegraph/eslint-config/builds/457#1b08014a-6f6a-4079-8f97-6d296ab8284d

There's some additional dev work to do in the Sourcegraph codebase before we can comfortably add this plugin. I think we can fix most of these relatively quickly, would be great to get this in soon

[github-actions]

Heads up @AlicjaSuska @felixfbecker @umpox @valerybugakov @5h1rU @pdubroy - the "team/frontend-platform" label was applied to this issue.