Update hierarchy docs for June 6, 2024

[aarongable]

Update the Chain of Trust and Certificate Compatibility pages to reflect the Let's Encrypt issuance hierarchy as of June 6, 2024, when we retire E1 and R3, and replace them with E5, E6, R10, and R11.

This PR is still a draft. TODO:

• [x] Update diagram at the top of Chain of Trust
• [x] Remove "Cross Signing" section, maybe move it to Compatibility page
• [x] Rewrite and/or move "Certificate Transparency" section
• [x] Add a section about the chains that our API provides
• [x] Update Compatibility page
• [x] Figure out how best to make the tests not complain about my <style> elements