Add preconnect resource hints for more components

When running a Lighthouse audit on an AMP page that contains an `amp-youtube` component in the first viewport, I saw a “Preconnect to required origins” warning:

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While AMP components already do `preconnect` in themselves, they do so _after_ the component script has loaded and ran. If we add `rel=preconnect` resource hint links to pages that have `amp-youtube` elements automatically, then we could shave some additional milliseconds and improve the Lighthouse score.