Update meta tags and sharing images

[rfultz]

What we're after:

It's been a while since we've reviewed the site's metadata tags and social media/sharing images and thumbnails.

The favicon on a darkmode desktop browser tab:

Mobile browser using the "The new FEC.gov" image:

• Google uses our general 'favicon' images but they're the "the new FEC.gov" images.
• Bing uses our general favicon images and puts them on a light background (at least if not switched to dark mode).
• DuckDuckGo uses our general favicon, too, but puts it on a dark background by default.

G	B	D

Related issues

#6564 fixes the canonical meta data tags

None

Completion criteria

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