Document Data Ingestion Pipeline

[michaelweinold]

The data ingestion pipeline must be documented (in the EcoPylot Sphinx documentation pages) before we start to implement

• https://github.com/sustainableaviation/EcoPyLot/issues/6

This documentation will then serve as the technical specification of the data ingestion pipeline.

[!NOTE]
This documentation is distinct from any API documentation (based on Python docstrings) that will be auto-generated from the data ingestion classes/functions. It should provide (technical) users a straightforward way to understand the data ingestion pipeline in the context of the entire project.

Ideally, this would include:

• [x] sample data (input/output)
• [x] a Mermaid diagram, if applicable
• [x] a short explanation of our choices behind the logic

[michaelweinold]

@iamsiddhantsahu, as discussed please start from the docs/content/structure.md file.