Add website version of April release notes

[raynamharris]

PR Checklist

• [x] Release label added
• [x] PR category label added
• [x] PR mergeable
• [x] Clean build logs
• [x] Linked related issues https://github.com/nih-cfde/training-and-engagement/issues/520
• [ ] Colorblindness test https://www.toptal.com/designers/colorfilter/

PR Description

This PR is getting the site ready for the April release. There will be no new lessons for this release. There is only one new website features. I want to merge this PR before merging dev into stable (unlike last time). This should make the process go more smoothly.

Preview link

https://cfde-training-and-engagement--526.com.readthedocs.build/en/526/

Timeline

This week. Release planned for April 15

[github-actions[bot]]

Reviewer Checklist

• [ ] spelling and grammar
• [ ] functional links (inter and intra)