Dependencies tree manager

[AlonZivony]

1. Explain what the PR does

Create a manager object for the dependencies between event.
It helps to follow what events are really used, and will enable to effectively cancel and add events and probes.

This is a first step towards my current goal of having fallbacks for dependencies, to have a proper solution for the process_execute_failed event.
I will create another PR after this one that support the fallback of dependencies, and afterwards work with it on the event.

The work on this PR exposed multiple problems or I might even call them bugs in our current code:

1. When an event fails, we just cancel all of its dependencies events even though they might be chosen or a dependency of another event. However, we don't cancel events that depend on it. This PR address this issue - Fix Events cancellation removes chosen dependencies events #3932
2. We don't cancel events properly upon failure. We don't detach their probes nor remove them from the policies filter maps. this wasn't addressed in this PR, but this PR exposes an easy way to do these things - using the watcher functions we can make sure to update everything upon each change to the events and their decencies. This PR does not address this issue, only creates the framework to solve it in future PRs

2. Explain how to test it

3. Other comments

[AlonZivony]

The current objects are not thread safe.
Do you want me to fix them to be or add some documentation about it?
Currently it doesn't matter, but in the future it might do.

[geyslan]

@AlonZivony I'll be on this soon.

[geyslan]

I reviewed the code and tests and didn't find any apparent flaws. I also ran the unit tests locally and checked the manager generated fields values with some prints. LGTM.

E2E 1433 is green. 👍🏼

Furthermore, put a few comments for discussion.

[yanivagman]

I'm going to review this soon. Please wait with merging it