Allow filters to supply OG tags for more types of queries

I wanted to add OG meta for a category query, but `$tags` only gets populated if `is_home()`, `is_front_page()`, `is_author()`, or `is_singular()`. Since after that the `$tags` is empty, the `jetpack_og_tags` function short circuits before the `jetpack_open_graph_tags` filter even gets a chance to run. So here I introduce a `jetpack_open_graph_base_tags` filter to allow metadata to be supplied for other query types. Alternatively, there is a `jetpack_open_graph_return_if_empty` filter which can be set to false to prevent the short-circuiting.