Limits the number of attempts to forward the request.
For the purpose of this limit, Squid counts all high-level request
forwarding attempts, including any same-destination retries after
certain persistent connection failures and any attempts to use a
different peer. However, these low-level attempts are not counted:
* connection reopening attempts (enabled using connect_retries)
* unfinished Happy Eyeballs connection attempts (prevented by setting
happy_eyeballs_connect_limit to 0)
See also: forward_timeout, connect_retries, and %request_attempts.