[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>

envipath/settings.py

@@ -45,6 +45,7 @@ INSTALLED_APPS = [
     "django.contrib.sessions",
     "django.contrib.messages",
     "django.contrib.staticfiles",
+    "django.contrib.postgres",
     # 3rd party
     "django_extensions",
     "oauth2_provider",
@@ -362,6 +363,10 @@ if SENTRY_ENABLED:
         before_send=before_send,
     )
 
+IUCLID_EXPORT_ENABLED = os.environ.get("IUCLID_EXPORT_ENABLED", "False") == "True"
+if IUCLID_EXPORT_ENABLED:
+    INSTALLED_APPS.append("epiuclid")
+
 # compile into digestible flags
 FLAGS = {
     "MODEL_BUILDING": MODEL_BUILDING_ENABLED,
@@ -370,6 +375,7 @@ FLAGS = {
     "SENTRY": SENTRY_ENABLED,
     "ENVIFORMER": ENVIFORMER_PRESENT,
     "APPLICABILITY_DOMAIN": APPLICABILITY_DOMAIN_ENABLED,
+    "IUCLID_EXPORT": IUCLID_EXPORT_ENABLED,
 }
 
 # path of the URL are checked via "startswith"