chore(events): Connect / DOWT template adjustments

Build Variables:

• Use Contentful Preview API

related: https://gitlab.com/gitlab-com/marketing/digital-experience/buyer-experience/-/issues/3434

Related: #3866 (closed)

Shoring up a few things so we can get this looking a little cleaner!

Review app:

https://connect-wt-template-fixes.about.gitlab-review.app/events/connect/gitlab-connect-melbourne-2024/