[Feature] Minimal IUCLID export (#338)

This is an initial implementation that creates a working minimal .i6z document.
It passes schema validation and can be imported into IUCLID.

Caveat:
IUCLID files target individual compounds.
Pathway is not actually covered by the format.

It can be added in either soil or water and soil OECD endpoints.
**I currently only implemented the soil endpoint for all data.**

This sort of works, and I can report all degradation products in a pathway (not a nice view, but we can report many transformation products and add a diagram attachment in the future).

Adding additional information is an absolute pain, as we need to explicitly map each type of information to the relevant OECD field.
I use the XSD scheme for validation, but unfortunately the IUCLID parser is not fully compliant and requires a specific order, etc.

The workflow is: finding the AI structure from the XSD scheme -> make the scheme validation pass -> upload to IUCLID to get obscure error messages -> guess what could be wrong -> repeat 💣

New specifications get released once per year, so we will have to update accordingly.
I believe that this should be a more expensive feature, as it requires significant effort to uphold.

Currently implemented for root compound only in SOIL:

- Soil Texture 2
- Soil Texture 1
- pH value
- Half-life per soil sample / scenario (mapped to disappearance; not sure about that).
- CEC
- Organic Matter (only Carbon)
- Moisture content
- Humidity

<img width="2123" alt="image.png" src="attachments/d29830e1-65ef-4136-8939-1825e0959c62">
<img width="2124" alt="image.png" src="attachments/ac9de2ac-bf68-4ba4-b40b-82f810a9de93">
<img width="2139" alt="image.png" src="attachments/5674c7e6-865e-420e-974a-6b825b331e6c">

Reviewed-on: enviPath/enviPy#338
Co-authored-by: Tobias O <tobias.olenyi@envipath.com>
Co-committed-by: Tobias O <tobias.olenyi@envipath.com>

epiuclid/api.py

@@ -0,0 +1,22 @@
+from uuid import UUID
+
+from django.http import HttpResponse
+from ninja import Router
+from epapi.v1.interfaces.iuclid.projections import get_pathway_for_iuclid_export
+
+from .serializers.i6z import I6ZSerializer
+from .serializers.pathway_mapper import PathwayMapper
+
+router = Router(tags=["iuclid"])
+
+
+@router.get("/pathway/{uuid:pathway_uuid}/export/iuclid")
+def export_pathway_iuclid(request, pathway_uuid: UUID):
+    export = get_pathway_for_iuclid_export(request.user, pathway_uuid)
+    bundle = PathwayMapper().map(export)
+    i6z_bytes = I6ZSerializer().serialize(bundle)
+    return HttpResponse(
+        i6z_bytes,
+        content_type="application/zip",
+        headers={"Content-Disposition": f'attachment; filename="pathway-{pathway_uuid}.i6z"'},
+    )