[Meta] Scan all public EUI docs pages for a11y violations and report regressions

[1Copenut]

Description

We're moving the component a11y tests into Cypress. Those tests will run on their own infrastructure and their own scheduled task outside the regular PR task. In doing so, we need new infrastructure and scheduled task to scan documentation pages for a11y violations.

This effort will be to identify and scope scanning public docs pages for accessibility at the page level. These will not test components directly, but will be a good sample size for testing multiple and composed components in full HTML pages.

Tasks

• Write a script to ingest public EUI docs pages and run a11y checks #6456
• Write a custom reporter to collect EUI docs a11y violations #6457
• Create a scheduled CI job to scan EUI docs #6458
• Add a Slack integration to notify on EUI docs a11y violations #6459
• Add a workflow to open GitHub issues on EUI docs a11y violations #6460