Improve handling of overlapping schedules

Checklist

[x] I checked for similar existing requests (both open and closed) before posting.
[x] My request is generic, other users may benefit from it too.

Background

I help to run a building where we run a number of clubs and other activities. So Club 1 might meet Friday at 5pm-7pm in room 1 then Club 2 might meet Friday 7pm-9pm and use rooms 1, 2 and 3.
So typically, we create a schedule entry for each club/event and schedule the heat to come on an hour or so before the actual event, then heat off at the end, so for room1, this would translate to be on at 4pm, off at 7pm and on at 6pm, off at 9pm. The problem is that the heating would go off at 7pm, when we want it still on.

Where the events are separated by more time, this method of scheduling is exactly what we want. But if for some reason a regular club isn't on one week, it can temporarily be turned of in the schedule, which is also why we don't just use a different schedule for each room to cover both clubs.

Proposal

If are overlapping schedules, with the later demanding heat, then a request from an earlier schedule to turn off should be ignored. Effectively the current heat setting should be the max of any concurrent schedules for a given entity.

Additional info

I think when the next even is the pending turn-off (which we don't want) the scheduler card should grey out the entry, and if possible give some indication that it is because it overlaps with another one.

nielsfaber / scheduler-component