Blog: Use `image` and `thumb` properties in post md header

[matijaSos]

There seems to be a possibility to define a cover image and the thumbnail for a blog post by using image and thumb properties. Check it out here (docusaurus docs) and here (blog post by Supabase: source, actual post)

So far, we've been manually adding a cover image for each blog post, which looking at the examples above, does not seem to be the right way to do it. I guess doing it Docusaurus way could also help with SEO and make sure the post summary is nicely displayed when shared on Twitter, LinkedIn, etc.