Accessibility tests

[nwmac]

Summary

Fixes #8986

Occurred changes and/or fixed issues

This PR is a re-work and update to #9457.

Technical notes summary

This PR adds a new e2e test suite a11y-tests which run a set of e2e tests with support for checking accessibility using the cypress-axe plugin.

This is done as a separate test suite, so that we get an easy-to-run suite that produces a single audit report, rather than the report being spread across multiple suites.

Checklist

• The PR is linked to an issue and the linked issue has a Milestone, or no issue is needed
• The PR has a Milestone
• The PR template has been filled out
• The PR has been self reviewed
• The PR has a reviewer assigned
• The PR has automated tests or clear instructions for manual tests and the linked issue has appropriate QA labels, or tests are not needed
• The PR has reviewed with UX and tested in light and dark mode, or there are no UX changes

[nwmac]

@aalves08 Can you take a look - would be good to get this in and then build out the tests

[rak-phillip]

My only critiques have to do with the formatting of the output. I'm finding it incredibly difficult to associate violations to test suites. For example, it appears that the output is formatted in such a way that information is grouped by:

1. Violation Count
2. Violations
3. Test Suite

When the next test suite starts, it bleeds into the rest of the information. Is there a better way that can group the output?