Implement Watcher

[kwiesmueller]

Key part of gorcon is to start and manage a games process and restart it if necessary.
This functionality is placed under the internal name "watcher" as the job of this package is to watch a process and monitor it's state implying actions on special events (which might also be external commands).

Implementation of this package should be very generic as usual and offer key functionality for starters.
This means opening an interface for starting, stopping and keeping processes alive.

Acceptance Criteria:

• Well defined and designed public API for
  • Starting a process
  • Keeping a process alive
  • Stopping a process
  • Subscribing event listeners for process output
• Functional passing on of context down the action tree for logging, tracing, etc.

Due to the general approach we follow with gorcon, event subscriptions should be handled by channels broadcasting all received process events to the subscribers.
This allows us to attach any kind of listener and allow them to act based on those events through the public API exposed by the watcher.

[kwiesmueller]

Remaining subtask at creation of this issue is the final implementation of process
process.go

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[kwiesmueller]

After spending the night on this, the process implementation is done, but due to some problems that arose with our tests in the subscription concept for both battleye and the watcher I started overthinking how this was built which might result in drastical changes to the subscription implementation or even an entire rewrite of watcher reducing the need of locks a lot.
Revisiting this part of code after some weeks helped to see the mess that looked so beautiful when it was created.

Updating this issue with further insights and probably a commit after some hours of sleep.

#7 is the related "Bugfix" issue

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[kwiesmueller]

The last push to master solved many problems related to this. Next step is plugging it with OSProcess, testing it in a running example and then finish up the feature with more refactoring.

[kwiesmueller]

Aside from that, Watcher implementation seems complete.

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