Expand .env capability to cover conceptual generation parameters such as embed model #39
Description
As noted in #38 (comment):
The constants in conceptual_generate.py starting with EMBED_MODEL_ID should probably be configurable. The proposed mechanism for doing that proposed in the comment above is:
- move the file docling_sdg/resources/watsonx_example.env to the root of the repository
- rename it to .env.example
- add this option with the feature name as prefix, e.g. CONCEPTUAL_GEN__EMBED_MODEL_ID with a default value (e.g., IBM Granite)
- leverage pydantic settings to parse nested variables.
- rename the existing Watsonx variables according to pydantic settings conventions for nested variables.
- update the documentation