Add a link to our terms of use in API response headers

As a small hint for users of our rest API, let’s add a X-Terms-of-Use header to the responses. It contains the URL of the “Terms of use for bulk access” web page.

swh/web/api/tests/test_apiresponse.py

@@ -152,6 +152,15 @@ def test_error_response_handler(mocker, api_client):
     assert "Traceback" in resp.data["traceback"]
 
 
+def test_tos_in_api_response_headers(api_client):
+    url = reverse("api-1-stat-counters")
+    response = api_client.get(url)
+    assert (
+        response.get("X-Terms-of-Use")
+        == "https://www.softwareheritage.org/legal/api-terms-of-use/"
+    )
+
+
 def test_api_endpoints_have_cors_headers(client, content, directory, revision):
     url = reverse("api-1-stat-counters")