R1:89778dc9e617

Add Open Graph protocol meta tags to Maniphest task pages

Summary:
Add OGP <meta> tags to Maniphest task pages when the task is publicly accessible and anonymously accessed. See https://ogp.me/

Based on rP2c72c2b924ffa3f8a49dbec636a2cdca3bae004f reverted in rP49b57eae7df52c189aef1d973823c697fc97fd4b.

Closes T15472

Test Plan:
* Use the default Phorge logo, open a Maniphest task, look at the headers in its HTML.
* Set a custom Phorge logo via `config/edit/ui.logo/`.
* Access a task with "View Policy: All…