add chat warning delay option

[PabloDinella]

I felt motivated to study a little bit of c++ with this project (I'm a web dev), so I tried to implement and propose a simple enhancement, which was already mentioned on #187 and #70.

The result is this option on Settings > Moderation:

Min value is 20 seconds, since below that is too spammy IMO, and max is 60.

There's something I didn't manage to change though: here we need to replace CHEATER_WARNING_INTERVAL with m_Settings->GetChatWarningInterval(), but I don't know how to use m_Settings here...

		// We also need to remove this in favor of m_Settings->GetChatWarningInterval()
		static constexpr duration_t CHEATER_WARNING_INTERVAL = std::chrono::seconds(20);

		// The soonest we can make an accusation after having seen an accusation in chat from a bot leader.
		// This must be longer than CHEATER_WARNING_INTERVAL.
		static constexpr duration_t CHEATER_WARNING_INTERVAL_NONLOCAL = CHEATER_WARNING_INTERVAL + std::chrono::seconds(10);