Transfer data blueprint

What does this MR do and why?

Contributes to https://gitlab.com/groups/gitlab-org/-/epics/7421

Create a blueprint for Transfer Data feature.

It covers the overall design and implementation only for Repository Egress.

Diagram from the document

flowchart TB

   A[Applications] -->|send logs| Pub(Google Pub/Sub)
   Pub -->|subscribe to topic|JSONParser
   

   subgraph DataFlowPipeline
      direction TB

      JSONParser -->|selects only JSON lines| LogProcessor
      LogProcessor -->|insert detected data transfer logs|ClickHouse
   end

ClickHouse -->|query transfer logs| Rails

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.