Fix og:image path to be absolute

[TristanCacqueray]

This change resolves the relative note image path to make an absolute url.

For blog/post.md with a ![img](media/image.png), the og:image is:

• Before: siteUrl/media/image.png
• After: siteUrl/blog/media/image.png

[srid]

cc @shivaraj-bh

[TristanCacqueray]

In any case, we need to tests before being able to make changes like this.

You are absolutely right, let me convert this to a draft. There are other papercuts in the og:description that I'd like to fix (like wikilink not being rendered properly and the footnote). Is there an example test we could use to validate such fixes?