Set timeout for DNS resolution in UrlBlocker
What does this MR do?
If DNS resolution takes a very long time, an HTTP request can exceed its time limit - in some cases significantly.
Ruby 2.7 adds a timeout keyword argument to Addrinfo.getaddrinfo. We
set that to the remaining time for the current request (if we're in a
request), bounded by zero on the lower end (so we don't try to set a
negative timeout), and five seconds on the upper end (as a reasonable
maximum).
This timeout argument only works on systems with getaddrinfo_a
available.
If the timeout is hit, Addrinfo.getaddrinfo raises a SocketError,
which is already handled correctly.