♻️(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/core/tests/test_services_converter_services.py

@@ -16,7 +16,7 @@ from core.services.converter_services import (
 
 def test_auth_header(settings):
     """Test authentication header generation."""
-    settings.CONVERSION_API_KEY = "test-key"
+    settings.Y_PROVIDER_API_KEY = "test-key"
     converter = YdocConverter()
     assert converter.auth_header == "test-key"
 
@@ -97,8 +97,9 @@ def test_convert_markdown_missing_content_field(mock_post, settings):
 def test_convert_markdown_full_integration(mock_post, settings):
     """Test full integration with all settings."""
 
-    settings.CONVERSION_API_URL = "http://test.com"
-    settings.CONVERSION_API_KEY = "test-key"
+    settings.Y_PROVIDER_API_BASE_URL = "http://test.com/"
+    settings.Y_PROVIDER_API_KEY = "test-key"
+    settings.CONVERSION_API_ENDPOINT = "conversion-endpoint"
     settings.CONVERSION_API_TIMEOUT = 5
     settings.CONVERSION_API_CONTENT_FIELD = "content"
 
@@ -113,7 +114,7 @@ def test_convert_markdown_full_integration(mock_post, settings):
 
     assert result == expected_content
     mock_post.assert_called_once_with(
-        "http://test.com",
+        "http://test.com/conversion-endpoint/",
         json={"content": "test markdown"},
         headers={
             "Authorization": "test-key",