enhance(opengraph): fix og:image and add og:{image:*,site_name,type}

[caugner]

Summary

Fixes #9429.

Problem

The Open Graph meta data had two issues:

1. The og:locale was not in the right format, with - instead of _ separating language and territory.
2. The og:image:alt property was missing.

Solution

1. Fix the og:locale format.
2. Add og:image:alt as well as og:image:{type,height,width}.

Also adds og:site_name and og:type.

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How did you test this change?

Ran yarn && yarn dev and inspected HTML of http://localhost:5042/zh-TW/docs/Learn/HTML.

[LeoMcA]

lgtm!