Create plugin to support Open Graph Protocol tags

[stuartmaxwell]

The Open Graph Protocol: https://ogp.me/

Should support the following four tags as a minimum:

• og:title - The title of your object as it should appear within the graph, e.g., "The Rock".
• og:type - The type of your object, e.g., "video.movie". Depending on the type you specify, other properties may also be required.
• og:image - An image URL which should represent your object within the graph.
• og:url - The canonical URL of your object that will be used as its permanent ID in the graph, e.g., "https://www.imdb.com/title/tt0117500/".

The reason this should be a plugin instead of core is that there are some interesting ways to create/generate the image which may require additional dependencies. If this becomes easier to implement than expected, I might consider bringing it into core.