add optional nginx configs to make more secure

Add back some items removed in https://github.com/gitlabhq/gitlabhq/commit/8aff39a6d0a63e904ada910900ee07a1c3190a9d but makes them optional so they can be ignored if you want a simple setup experience.
@dosire @bbodenmiller Thanks for involving me in this discussion. It is entirely up to the Gitlab BV team to decide wether they want to recommend OCSP stapling or not.