Move OG tags from Sharing module to core

[allanaaa]

Lots of our users probably want their Omeka links to embed nicely on social media pages. Few of them are going to learn what cards are, what Open Graph tags are, and how they are generated, then look through our modules and docs, figure out that Sharing will do it (which I still frequently confuse with Resource Meta when looking for it), install it, and then uncheck everything in the settings of each site so they get the meta functions without the visible buttons.

Could we move OG tag generation into the core in future versions? It could be turned on or off on a site basis, or install-wide.