Enable "delayed events" by default

[spaetz]

Given delayed_events solve the problem of stuck element-call calls and there is hardly any downside to enabling them, please consider setting

max_event_delay_duration: 24h

as the default. RIght now they are disabled by default.

Reference MSC4140

[erikjohnston]

Hi, generally we have a policy that we don't enable experimental features by default (though we do occasionally do so), to avoid these sort of features becoming "de facto specced". Not least, this tends to lead to features never finishing the MSC process as there is less impetus to do so.

Let me have a poke as to what is happening with MSC4140, ideally we'd "just" push it over the line instead.