45 reduce org file

[germankay]

First, review the PR: Reduce file size

related #45

Refactor of organisation_xml_generator.py
Changes

The organisation_xml_generator.py file has been reorganized into a modular structure to improve maintainability, readability, and separation of responsibilities.

New package organization:

src/okfn_iati/

├── organisations/
    ├── base.py
    ├── process_csv/
    │   └── builders.py
    └── process_xml/
        └── extractors.py