Raise max objective guests to 50000

[Gymnasiast]

Requested in the Discord chat.

Closes #15849.

[ZeeMaji]

65000 seems a bit too high imo, wouldn't that only leave about 500 entity slots open for vehicles, staff, balloons, ducks, etc?
I feel like that'd be something you'd hit pretty fast in a park designed to contain that many guests.
I think 50000 would be a bit more reasonable as that would give a good buffer of about 15000 entities between the max objective cap and the entity limit.

I also think it would be a good idea to raise the 7000 guest soft cap in openrct2/world/Park.cpp as it was clearly designed with the old objective & entity limits in mind, probably setting that to a number around 57000 would make the most sense as that's a number roughly between the max objective cap and the entity limit similar to how it was with the vanilla limits. Or would that be out of the scope of this PR?

[Gymnasiast]

I think that would be out of scope, though that’s ultimately for the team to say.

[Broxzier]

50,000 is a good compromise, which also doesn't seem like a magic number to the players.