Add Open Graph tags for published charts

[bprusinowski]

Currently we do not have any picture attached to a preview of the page when sharing a link to a published chart e.g. on social media. It could be a nice addition to be able to see a chart in the image field, as well as chart title and description.

See e.g. https://www.opengraph.xyz/url/https%3A%2F%2Fvisualize.admin.ch%2Fen%2Fv%2FCKdwKBmwkit8

[ptbrowne]

https://vercel.com/docs/concepts/functions/edge-functions/og-image-generation could be interesting