Make UNIX socket the default

I think using a unix socket should be the default for notify_push, as it is both more efficient (which is what notify_push is about) and more secure (as access can be limited to the local www-data user).
To do so I would suggest a couple of issues to be considered:

• what is the default location and mask for the socket? I would suggest a location in a subdir of the notify_push folder, and a mask of 660 (instead of 666); as a result it will be read/writeable to www-data only on default installations of nextcloud
• the notify_push.service difnition will have to be updated to set a socket rather than a port
• the nginx location definition should use proxy_pass http://unix:/path_to/notify_push.sock:/; (anyone a suggestion for the corresponding Apache config?)

I think this is a fairly minor update which will make notify_push better.

Start by reviewing the notify_push.service definition and the existing nginx location configuration mentioned in the issue. Resolve the default Unix socket location and mask, then determine the corresponding Apache configuration. The work is done when notify_push defaults to a Unix socket and the service and reverse-proxy configurations consistently use it.