Add more details to what _MAX_AHEAD_SCHEDULE is for

[llucax]

I didn't understand which issue this is trying to solve, maybe we need a more detailed explanation of the issue and how this solves it.

Originally posted by @llucax in #9 (comment)

[Marenz]

Is the existing documentation sufficient?

frequenz-dispatch-python/src/frequenz/dispatch/actor.py

Line 27 in 8e53a3b

The exact value is not important, but should be a few hours and not more than a day.

[llucax]

To me, no. That doesn't say what is it for and what's the effect on changing it.

[Marenz]

Really? What more would you need from the description?

"""The maximum time ahead to schedule a dispatch.

We don't want to schedule dispatches too far ahead,
as they could start drifting if the delay is too long.

This also prevents us from scheduling too many dispatches at once.

The exact value is not important, but should be a few hours and not more than a day.

It describes the effect if it's too long and why it's there?

[llucax]

Reading the whole description doesn't help a lot. What does it mean to "schedule a dispatch too far ahead" (or just "ahead")? I don't understand if you are scheduling the dispatches in the future? Also what does it mean exactly to "schedule a dispatch", it means you add it to some list so it is checked periodically to see if it ready to run or what?

Also drifting with respect to what? Why does this prevents scheduling too many dispatches at once?

I think a time diagram might help here, but I'm still uncertain because I still don't understand what this does :P