ECDC-3618 add observer pattern to commons

Created by: tbukovics

Issue reference / description

Add templates to implement the observer pattern, which will be used by timepix to make possible fluent data event handling and processing independent from the parser. Simple flow chart how event based dataflow would look with the observer.

flowchart LR;
    A[RingBuffer Data Input] -->|Data| B{Data Parser}
    B -->|PIXEL Data| C[PIXEL Publisher]
    B -->|TDC Data| D[TDC Publisher]
    B -->|EVR Data| E[EVR Publisher]

    TimingEventHandler{TimingEventHandler}
    PixelEventHandler{PixelEventHandler}

    D -.-> |subscribe| TimingEventHandler
    E -.-> |subscribe| TimingEventHandler

    TimingEventHandler --- PixelEventHandler
    C -.-> |subscribe| PixelEventHandler

Checklist for submitter

• Check for conflict with integration test
• Unit tests pass

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