[INFRA] Add a workflow to check the accessibility of the website from the preview of a PR

[csouchet]

Some POCs has been done:

• foo-software/lighthouse-check-action  chore(poc): add a new workflow for the foo-software/lighthouse-check-action action #1166
• a11ywatch/github-action chore(poc): add a new workflow for the a11ywatch/github-action #1165
• a11ytester-action chore(poc): add a new workflow for the a11ytester-action action #1164
• axe-core/cli chore(poc): add a new workflow for axe-core/cli #1163
• Pa11y CI chore(poc): add a new workflow for Pa11y CI #1162
• treosh/lighthouse-ci-action chore(poc): add a new workflow for the treosh/lighthouse-ci-action action #1161