option to send the access log to stdout

[Igor Bukanov]

When nginx runs in a container or under a process manager that provide own logging facilities or to prevent the nginx process from manipulate the written log it would be useful if the access_log directive supported setting the log path to stdout similarly as error_log allows to send the log to stderr.

As a workaround in some cases one can use access_log /dev/stdout or similar. However, as nginx calls open() on the supplied path that may fail depending on how the receiving end of stderr and its permissions is set up. A better workaround is to use mkfifo to create a named pipe and then use cat /path-to-pipe to send the log out, but this is messy.