Add OpenGraph meta tags

[Jean85]

Description

This PR adds generig OpenGraph meta tags, using normal configuration parameters.

Motivation and Context

I reworked the theme of our blog in a proper fork: https://github.com/facile-it/hugo-future-imperfect
I'm reporting upstream this change.

How Has This Been Tested?

This modification is currently in production on our blog: https://engineering.facile.it/

Hugo Version: 0.31.1

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the [code style] of this project.
• My change requires a change to the [documentation].
• I have updated the documentation, including theme.toml, accordingly.
• I have read the [Contributing Document].

[pacollins]

Thanks for this addition! It might be worthwhile to add this to the article/image templates as well.