Add accessibility linting

[dfarrell07]

Add linting to verify the accessibility of Submariner's website content.

We need to do some research on which tooling is best, but https://github.com/dequelabs/axe-core seems like a good toolkit, and the list of projects that consume it seems like good next place to look https://github.com/dequelabs/axe-core/blob/develop/doc/projects.md.

[stale]

This issue has been automatically marked as stale because it has not had activity for 60 days. It will be closed if no further activity occurs. Please make a comment if this issue/pr is still valid. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had activity for 60 days. It will be closed if no further activity occurs. Please make a comment if this issue/pr is still valid. Thank you for your contributions.