Include axe automated accessibility checks in GitLab UI and write tests for components
## Goal
Run the [axe core accessibility testing engine](https://github.com/dequelabs/axe-core) on Pajamas and other GitLab UI components to identify accessibility problems and prevent regressions.
## Technical strategy
### Create a test coverage issue
1. Select a component from the _Components_ section at https://design.gitlab.com/.
2. Create an issue using the automated accessibility test [issue template](https://gitlab.com/gitlab-org/gitlab-ui/-/blob/main/.gitlab/issue_templates/AutomatedAccessibilityTest.md?ref_type=heads) in the GitLab UI project.
3. Visit the component's [Storybook](https://gitlab-org.gitlab.io/gitlab-ui/) page and identify all the states that require an accessibility test.
4. Document those states in the issue created in Step 2.
### Implementing test coverage
Follow the instructions described in the axe [accessibility tests documentation](https://gitlab.com/gitlab-org/gitlab-ui/-/blob/main/doc/contributing/end_to_end_test.md?ref_type=heads#axe-accessibility-tests) to implement an accessibility component test.
## Progress tracking
For current progress status, [visit our dashboard](https://epic-dashboard-gitlab-org-tenant-scale-group-4aecf10d1d02154641.gitlab.io/epic_11090)
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