Re-enable cassava-megaparsec, email-validate, yesod, yesod-form

[simonmichael]

Checklist:

• Meaningful commit message, eg add my-cool-package (please don't mention build-constraints.yml)
• At least 30 minutes have passed since uploading to Hackage
• If applicable, required system libraries are added to 02-apt-get-install.sh or 03-custom-install.sh
• (optional) Package is compatible with the latest version of all dependencies (Run cabal update && cabal outdated)
• (optional) Package have been verified to work with the latest nightly snapshot, e.g by running the verify-package script

[ysangkok]

This doesn't seem to address all the packages that need yesod or yesod-form. Would it be possible to re-enable those too?
You can see how in CURATORS.md's section on re-enabling.

[simonmichael]

I could have done that, but then I'd be responsible for testing and getting all of those to work, potentially delaying getting my packages working again. I figured I would send a followup PR for that.

[simonmichael]

But if you'd prefer I do it all in this one, I will.

[ysangkok]

I can do it in a separate PR if you'd rather not.

[simonmichael]

Ok, thank you @ysangkok.