♻️(backend) generalize YProvider API config

Abstracted base URL and API key under 'y-provider' for
reuse in future endpoints, aligning with microservice naming.

Please note the YProvider API here is internal to the cluster.
In facts, we don't want these endpoints to be exposed by any ingress

src/backend/impress/settings.py

@@ -505,13 +505,21 @@ class Base(Configuration):
         "day": 200,
     }
 
-    # Conversion microservice
-    CONVERSION_API_KEY = values.Value(
-        environ_name="CONVERSION_API_KEY",
+    # Y provider microservice
+    # Note: Be careful, this value is currently the same as in the collaboration service.
+    Y_PROVIDER_API_KEY = values.Value(
+        environ_name="Y_PROVIDER_API_KEY",
         environ_prefix=None,
     )
-    CONVERSION_API_URL = values.Value(
-        environ_name="CONVERSION_API_URL",
+    Y_PROVIDER_API_BASE_URL = values.Value(
+        environ_name="Y_PROVIDER_API_BASE_URL",
+        environ_prefix=None,
+    )
+
+    # Conversion endpoint
+    CONVERSION_API_ENDPOINT = values.Value(
+        default="convert-markdown",
+        environ_name="CONVERSION_API_ENDPOINT",
         environ_prefix=None,
     )
     CONVERSION_API_CONTENT_FIELD = values.Value(