Document CI long polling settings
From gitlab-workhorse!687 (comment 519677581), it appears we haven't documented CI long polling anywhere, and it is effectively disabled by default since the default hold time is 50 ns instead of 50 s.
We should start by documenting api_ci_long_polling_duration
. Setting it to 0 will effectively disable it. Setting it to 50s
(50 seconds) will mean runners will wait for 50 s before the request gets forwarded to GitLab Rails.