Support injecting random delay when clients connect via DelayOnEvent

[Castaglia]

Currently, it is possible to inject delays at certain points during the lifecycle of a session via the DelayOnEvent directive from the mod_delay module. The scope of this feature request is to allow injecting delays, in a similar manner, to the very start of session, such as when it connects.

There are some busy sites where many clients connect in a very short period of time. It can be beneficial to spread the handling of those client connections out over a larger time window. By injecting delays at the start of the session, such spreading out can be achieved server-side.

In addition, we will want to inject a random (or jittered) amount of time, so that different clients get different delays. Currently, the DelayOnEvent directive expects a static single amount of time; for our use case, being able to configure a range of time, min/max, is more useful. The module would then randomly select a value from within that range to use as the delay duration.

[Castaglia]

This feature is now available in master.