Code enhancements for future use

[yhabteab]

This PR proposes the following improvements in preparation for #188.

• 9502b20958f6cbd085952a41e8c05b771096ebda decouples contactChannels from the incident package, since we're going to use this recipient channels map elsewhere outside the incident package in the future and it seems reasonable to me to move it here to the rule package.
• d238b0bf33cf0781a2965745f27ccc88fa20d6a4 implements zapcore.ObjectMarshaler for the rule.Escalation and recipient.Key types and allows us to use zap.Inline(escalation) or zap.Object("escalation", escalation)wherever more logging context is needed without having to add all the individual fields ourselves each time.
• ce8732e7e5de9739a11621293da9e743e1e43233 moves the ErrSuperfluousStateChange error type to the event package in order to mitigate a cyclic import error with the upcoming changes to non-state event processing support. It kind of also fit into this package.
• 706ed389af7c054545662405965900a00839fae1 drops incident#AddHistory() method as it was already quite annoying having to return types.Int every single time this method was used. This commit embeds the functionality for insert and fetch ID directly into the HistoryRow type and nowhere needs to be returned.
• 7ef9aa25f3b82bc8076bca4f5ec483661f0c66ae drops the create param from incident#ProcessEvent() and incident#GetCurrent(), since we can easily determine whether an incident is new based on its StartedAt timestamp, and thus, we don't need to pass this info around methods. (Added @sukhwinder33445 as a co-author as the original idea was from him, but I've implemented it in a slightly different way).

[yhabteab]

The output of zap.Object("escalation", escalation) looks as follows:

2024-05-17T10:05:49.375+0200    INFO    incident        Rule reached escalation {"object": "icinga-2!ping4", "incident": "#12", "rule": "default", "escalation": {"id": 1, "rule_id": 1, "name": "[S] Working Hours, [C] Yonas Habteab", "condition": "incident_severity>=ok"}}