Use Docsy-friendly section partial

[lmktfy]

Use a partial for <section> that will work with near-vanilla Docsy.

Helps with issue #41171.

Preview of the updated page.

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[lmktfy]

There are two kinds of CSS change.

1. Fixes for the video section to make it display about right after the update.
2. Hiding the KubeWeekly sign up link (see Update site landing page #51829)

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[lmktfy]

Oh, hmm. It worked on my machine when I previewed it.

/retitle [WIP] Use Docsy-friendly section partial

[lmktfy]

/retitle Use Docsy-friendly section partial

@dipesh-rawat @natalisucks this is ready for a review (I hope - it works on my machine)