upload default share image, remove unnecessary meta tag front matter

[hazel-nut]

summary

• update the default share image:

  • remove manual deep links to the old cdn from front matter and upload the image to this repo
  • delete unnecessary og:image front matter and set the default share image in the site config

• remove unnecessary meta tag front matter:

  • og:title and twitter:title are set from title
  • og:description and twitter:description are set from description
  • og:url is generated automatically from the canonical URL, which is built from the page URL

• remove permalink front matter because it doesn't do anything (page URLs are determined by path and filename)

testing

• compare the meta tags in page source from builds off this branch with meta tags in prod and see that they're the same
• build locally, change a permalink, and see that the URL of the page doesn't change
• make sure the new share image is correctly being served

[mikemimik]

A different approach to a wide change like this, might be to contain it to a single folder and it's sibling translation folders. This way we can validate the change on a small scale, and then introduce many smaller pull-requests all introducing the same change to limit the risk of each pull-request.

@hazel-nut what do you think about decomposing this pull-request into many smaller pull-requests?

[hazel-nut]

@mikemimik not an issue if you prefer. i broke up this PR into more granular commits per top-level docs directory to give you an idea of each diff with that approach. if that seems okay to you, i can close this PR and open a dozen or so smaller corresponding ones.